Abstract

XML is a versatile markup language, capable of
labeling the information content of diverse data sources including
structured and semi-structured documents, relational databases, and
object repositories. A query language that uses the structure of
XML intelligently can express queries across all these kinds of
data, whether physically stored in XML or viewed as XML via
middleware. This specification describes a query language called
XQuery, which is designed to be broadly applicable across many
types of XML data sources.

XQuery 1.1 is an extended version of the XQuery
1.0 Recommendation published on 23 January 2007. A list of changes
made since XQuery 1.0 can be found in K Revision Log. Here are some of the
new features in XQuery 1.1:

Status of this Document

This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest
revision of this technical report can be found in the W3C technical reports index at
http://www.w3.org/TR/.

This is one document in a set of seven documents that are being
progressed to Recommendation together (XQuery 1.1, XQueryX 1.1,
XSLT 2.1, Data Model 1.1, Functions and Operators 1.1,
Serialization 1.1, XPath 2.1).

A considerable number of changes have been made to this document
since publication of the previous Working Draft. Among the most
notable of those changes are: the addition of higher-order
functions to the language; the addition of private functions to the
language; changes to the context item declaration, the ability to
specify the types of external variables, and the addition of a new
switch expression analogous to the existing typeswitch expressions
(but for values).

The WG requests priority feedback on the question of whether the
grouping variables in the post-grouping tuple should contain the
grouping key for a grouping variable in a pre-grouping tuple, which
is atomized, rather than the value of the grouping variable in a
pre-grouping tuple. See 3.8.7 Group By
Clause.

No implementation report currently exists. However, a Test Suite
for XQuery 1.1 is under development.

This document incorporates changes made against the previous
publication of the Working Draft of 03 December 2008. Changes to
this document since the previous publication of the Working Draft
are detailed in K Revision
Log.

Publication as a Working Draft does not imply endorsement by the
W3C Membership. This is a draft document and may be updated,
replaced or obsoleted by other documents at any time. It is
inappropriate to cite this document as other than work in
progress.

1
Introduction

As increasing amounts of information are stored,
exchanged, and presented using XML, the ability to intelligently
query XML data sources becomes increasingly important. One of the
great strengths of XML is its flexibility in representing many
different kinds of information from diverse sources. To exploit
this flexibility, an XML query language must provide features for
retrieving and interpreting information from these diverse
sources.

XQuery is designed to meet the requirements
identified by the W3C XML Query Working Group [XQuery 1.1 Requirements] and the use
cases in [XML Query Use Cases]. It is
designed to be a language in which queries are concise and easily
understood. It is also flexible enough to query a broad spectrum of
XML information sources, including both databases and documents.
The Query Working Group has identified a requirement for both a
non-XML query syntax and an XML-based query syntax. XQuery is
designed to meet the first of these requirements. XQuery is derived
from an XML query language called Quilt [Quilt], which in turn borrowed features from several
other languages, including XPath 1.0 [XML Path
Language (XPath) Version 1.0], XQL [XQL],
XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].

XQuery Version 1.1 is an extension of XPath Version 2.1. In
general, any expression that is syntactically valid and executes
successfully in both XPath 2.1 and XQuery 1.1 will return the same
result in both languages. There are a few exceptions to this
rule:

Because XQuery expands predefined entity references
and character references and XPath
does not, expressions containing these produce different results in
the two languages. For instance, the value of the string literal
"&amp;" is & in XQuery, and
&amp; in XPath. (XPath is often embedded in other
languages, which may expand predefined entity references or
character references before the XPath expression is evaluated.)

If XPath 1.0 compatibility mode is enabled, XPath behaves
differently from XQuery in a number of ways, which are discussed in [XML Path
Language (XPath) 2.1].

Because these languages are so closely related, their grammars
and language descriptions are generated from a common source to
ensure consistency, and the editors of these specifications work
together closely.

XQuery 1.1 also depends on and is closely related to the
following specifications:

One requirement in [XQuery 1.1
Requirements] is that an XML query language have both a
human-readable syntax and an XML-based syntax. The XML-based syntax
for XQuery is described in [XQueryX
1.1].

[Definition: An XQuery 1.1
Processor processes a query according to the XQuery 1.1
specification.]

[Definition: An XQuery 1.0
Processor processes a query according to the XQuery 1.0
specification.]

This document specifies a grammar for XQuery 1.1, using the same
basic EBNF notation used in [XML 1.0]. Unless
otherwise noted (see A.2 Lexical
structure), whitespace is not significant in queries. Grammar productions are introduced
together with the features that they describe, and a complete
grammar is also presented in the appendix [A
XQuery 1.1 Grammar]. The appendix is the normative
version.

In the grammar productions in this document, named symbols are
underlined and literal text is enclosed in double quotes. For
example, the following production describes the syntax of a
function call:

The production should be read as follows: A function call
consists of a QName followed by an open-parenthesis. The
open-parenthesis is followed by an optional argument list. The
argument list (if present) consists of one or more expressions,
separated by commas. The optional argument list is followed by a
close-parenthesis.

This document normatively defines the static and dynamic
semantics of XQuery 1.1. In this document, examples and material
labeled as "Note" are provided for explanatory purposes and are not
normative.

Certain aspects of language processing are described in this
specification as implementation-defined or
implementation-dependent.

[Definition:
Implementation-defined indicates an aspect that may differ
between implementations, but must be specified by the implementor
for each particular implementation.]

[Definition:
Implementation-dependent indicates an aspect that may differ
between implementations, is not specified by this or any W3C
specification, and is not required to be specified by the
implementor for any particular implementation.]

2 Basics

The basic building block of XQuery 1.1 is the expression,
which is a string of [Unicode] characters
(the version of Unicode to be used is implementation-defined.) The
language provides several kinds of expressions which may be
constructed from keywords, symbols, and operands. In general, the
operands of an expression are other expressions. XQuery 1.1 allows
expressions to be nested with full generality. (However, unlike a pure functional language, it does not
allow variable substitution if the variable declaration contains
construction of new nodes.)

Note:

This specification contains no assumptions or requirements
regarding the character set encoding of strings of [Unicode] characters.

Like XML, XQuery 1.1 is a case-sensitive language. Keywords in
XQuery 1.1 use lower-case characters and are not reserved—that is,
names in XQuery 1.1 expressions are allowed to be the same as
language keywords, except for certain unprefixed function-names
listed in A.3 Reserved Function
Names.

[Definition:
In the data model, a
value is always a sequence.] [Definition: A sequence is an ordered
collection of zero or more items.] [Definition: An item is either an atomic value or a
node.] [Definition: An
atomic value is a value in the value space of an atomic
type, as defined in [XML Schema].]
[Definition: A
node is an instance of one of the node kinds defined
in [XQuery and XPath Data Model (XDM)
1.1].] Each node has a unique node identity, a typed
value, and a string value. In addition, some nodes have
a name. The typed value of a node is a sequence of
zero or more atomic values. The string value of a node is a
value of type xs:string. The name of a node is
a value of type xs:QName. [Definition: In certain
situations a value is said to be undefined (for example, the
value of the context item, or the typed value of an element node).
This term indicates that the property in question has no value and
that any attempt to use its value results in an error.]

[Definition: A sequence containing exactly one
item is called a singleton.] An item is identical to a
singleton sequence containing that item. Sequences are never
nested—for example, combining the values 1, (2, 3), and ( ) into a
single sequence results in the sequence (1, 2, 3). [Definition: A sequence containing zero
items is called an empty sequence.]

Names in XQuery 1.1 are called QNames, and conform to the
syntax in [XML Names]. [Definition: Lexically, a
QName consists of an optional namespace prefix and a local
name. If the namespace prefix is present, it is separated from the
local name by a colon.] A lexical QName can be converted into an
expanded QName by resolving its namespace prefix to a
namespace URI, using the statically known namespaces
[err:XPST0081].
[Definition: An expanded QName
consists of an optional namespace URI and a local name. An expanded
QName also retains its original namespace prefix (if any), to
facilitate casting the expanded QName into a string.] The namespace
URI value is whitespace normalized according to the rules for the
xs:anyURI type in [XML
Schema]. Two expanded QNames are equal if their namespace URIs
are equal and their local names are equal (even if their namespace
prefixes are not equal). Namespace URIs and local names are
compared on a codepoint basis, without further normalization.

Certain namespace prefixes are predeclared by
XQuery and bound to fixed namespace URIs. These namespace prefixes
are as follows:

In addition to the prefixes in the above list,
this document uses the prefix err to represent the
namespace URI http://www.w3.org/2005/xqt-errors (see
2.3.2 Identifying and Reporting
Errors). This namespace prefix is not predeclared and its
use in this document is not normative.

Element nodes have a property called in-scope namespaces.
[Definition: The in-scope
namespaces property of an element node is a set of namespace
bindings, each of which associates a namespace prefix with a
URI, thus defining the set of namespace prefixes that are available
for interpreting QNames within the scope of the element. For a
given element, one namespace binding may have an empty prefix; the
URI of this namespace binding is the default namespace within the
scope of the element.]

Note:

In [XML Path Language (XPath) Version 1.0],
the in-scope namespaces of an element node are represented by a
collection of namespace nodes arranged on a namespace
axis, which is optional and deprecated in [XML Path Language (XPath) 2.1]. XQuery does not
support the namespace axis and does not represent namespace
bindings in the form of nodes. However, where other specifications
such as [XSLT and XQuery
Serialization 1.1] refer to namespace nodes, these nodes may be
synthesized from the in-scope namespaces of an element node by
interpreting each namespace binding as a namespace node.

[Definition: Within
this specification, the term URI refers to a Universal
Resource Identifier as defined in [RFC3986]
and extended in [RFC3987] with the new name
IRI.] The term URI has been retained in preference to IRI to
avoid introducing new names for concepts such as "Base URI" that
are defined or referenced across the whole family of XML
specifications.

2.1 Expression Context

[Definition: The expression
context for a given expression consists of all the information
that can affect the result of the expression.] This information is
organized into two categories called the static context and the dynamic
context.

2.1.1 Static
Context

[Definition: The static context of an
expression is the information that is available during static
analysis of the expression, prior to its evaluation.] This
information can be used to decide whether the expression contains a
static error.
If analysis of an expression relies on some component of the
static
context that has not been assigned a value, a static error is raised
[err:XPST0001].

[Definition:
XPath 1.0 compatibility mode.This
component must be set by all host languages that include XPath 2.1
as a subset, indicating whether rules for compatibility with XPath
1.0 are in effect. XQuery sets the value of this component to
false. ]

[Definition:
Statically known namespaces. This is a set of (prefix, URI)
pairs that define all the namespaces that are known during static
processing of a given expression.] The URI value is whitespace
normalized according to the rules for the xs:anyURI
type in [XML Schema]. Note the difference
between in-scope namespaces, which is a
dynamic property of an element node, and statically known namespaces, which is a
static property of an expression.

[Definition:
Default element/type namespace. This is a namespace URI or
"none". The namespace URI, if present, is used for any unprefixed
QName appearing in a position where an element or type name is
expected.] The URI value is whitespace normalized according to the
rules for the xs:anyURI type in [XML Schema].

[Definition: Default function namespace.
This is a namespace URI or "none". The namespace URI, if present,
is used for any unprefixed QName appearing in a position where a
function name is expected.] The URI value is whitespace normalized
according to the rules for the xs:anyURI type in
[XML Schema].

[Definition: In-scope schema definitions. This
is a generic term for all the element declarations, attribute
declarations, and schema type definitions that are in scope during
processing of an expression.] It includes the following three
parts:

[Definition: In-scope element declarations.
Each element declaration is identified either by an expanded QName (for
a top-level element declaration) or by an implementation-dependent element
identifier (for a local element declaration). If the Schema Import Feature is supported,
in-scope element declarations include all element declarations
found in imported schemas. ] An element declaration includes
information about the element's substitution group affiliation.

[Definition: Substitution groups
are defined in [XML Schema] Part 1,
Section 2.2.2.2. Informally, the substitution group headed by a
given element (called the head element) consists of the set
of elements that can be substituted for the head element without
affecting the outcome of schema validation.]

[Definition: In-scope attribute
declarations. Each attribute declaration is identified either
by an expanded
QName (for a top-level attribute declaration) or by an
implementation-dependent
attribute identifier (for a local attribute declaration).
If the Schema Import Feature is supported,
in-scope attribute declarations include all attribute declarations
found in imported schemas. ]

[Definition: In-scope variables.
This is a set of (expanded QName, type) pairs. It defines the set
of variables that are available for reference within an expression.
The expanded
QName is the name of the variable, and the type is the
static type of
the variable.]

Variable declarations in a Prolog are added to in-scope
variables. An expression that binds a variable (such as
a let, for, some, or
every expression) extends the in-scope
variables of its subexpressions with the new bound variable and
its type. Within a function
declaration, the in-scope variables are extended by the
names and types of the function parameters.

The static type of a variable may either be
declared in a query or inferred by static type inference as
discussed in 5.2.3 Static
Typing Feature.

[Definition: Context item
static type. This component defines the static type of the context item within
the scope of a given expression.]

[Definition: Function signatures.
This component defines the set of functions that are available to
be called from within an expression. Each function is uniquely
identified by its expanded QName and its arity (number of
parameters).] In addition to the name and arity, each function
signature specifies the static types of the function parameters and
result.

[Definition: Default collation. This
identifies one of the collations in statically known collations as the
collation to be used by functions and operators for comparing and
ordering values of type xs:string and
xs:anyURI (and types derived from them) when no
explicit collation is specified.]

[Definition: Construction mode.
The construction mode governs the behavior of element and document
node constructors. If construction mode is preserve,
the type of a constructed element node is xs:anyType,
and all attribute and element nodes copied during node construction
retain their original types. If construction mode is
strip, the type of a constructed element node is
xs:untyped; all element nodes copied during node
construction receive the type xs:untyped, and all
attribute nodes copied during node construction receive the type
xs:untypedAtomic.]

[Definition: Ordering mode. Ordering
mode, which has the value ordered or
unordered, affects the ordering of the result sequence
returned by certain path expressions, FLWOR expressions, and
union, intersect, and except
expressions.] Details are provided in the descriptions of these
expressions.

[Definition: Default order for empty
sequences. This component controls the processing of empty
sequences and NaN values as ordering keys in an
order by clause in a FLWOR expression, as described in
3.8.8 Order By Clause.]
Its value may be greatest or least.

[Definition: Copy-namespaces
mode. This component controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor, as described in 3.7.1 Direct Element
Constructors. Its value consists of two parts:
preserve or no-preserve, and
inherit or no-inherit.]

[Definition: Base URI. This is an absolute
URI, used when necessary in the resolution of relative URIs (for
example, by the fn:resolve-uri function.)] The URI
value is whitespace normalized according to the rules for the
xs:anyURI type in [XML
Schema].

[Definition: Statically known documents.
This is a mapping from strings onto types. The string represents
the absolute URI of a resource that is potentially available using
the fn:doc function. The type is the static type of a call to
fn:doc with the given URI as its literal argument. ]
If the argument to fn:doc is a string literal that is
not present in statically known documents, then the
static type of
fn:doc is document-node()?.

Note:

The purpose of the statically known documents is to
provide static type information, not to determine which documents
are available. A URI need not be found in the statically known
documents to be accessed using fn:doc.

[Definition:
Statically known collections. This is a mapping from strings
onto types. The string represents the absolute URI of a resource
that is potentially available using the fn:collection
function. The type is the type of the sequence of nodes that would
result from calling the fn:collection function with
this URI as its argument.] If the argument to
fn:collection is a string literal that is not present
in statically known collections, then the static type of
fn:collection is node()*.

Note:

The purpose of the statically known collections is to
provide static type information, not to determine which collections
are available. A URI need not be found in the statically known
collections to be accessed using
fn:collection.

[Definition: Statically known
default collection type. This is the type of the sequence of
nodes that would result from calling the fn:collection
function with no arguments.] Unless initialized to some other value
by an implementation, the value of statically known default
collection type is node()*.

[Definition: Statically known
decimal formats. This is the set of known decimal formats. Each
format is used for serializing decimal numbers using
fn:format-number().] Each format is identified by a
QName, except for the default format, which has no visible name.
Each format contains the properties described in the following
paragraphs.

The following properties control the interpretation of
characters in the picture string supplied to the
fn:format-number function, and also specify characters
that may appear in the result of formatting the number. In each
case the value must be a single character (see [err:XQST0100]):

[Definition:
decimal-separator specifies the character used for the
decimal-separator-sign; the default value is the period character
(.)]

[Definition:
grouping-separator specifies the character used for the
grouping-sign, which is typically used as a thousands separator;
the default value is the comma character (,)]

[Definition:
percent-sign specifies the character used for the
percent-sign; the default value is the percent character (%)]

[Definition:
per-mille-sign specifies the character used for the
per-mille-sign; the default value is the Unicode per-mille
character (#x2030)]

[Definition:
zero-digit specifies the character used for the
digit-zero-sign; the default value is the digit zero (0). This
character must be a digit (category Nd in the Unicode property
database), and it must have the numeric value zero. This attribute
implicitly defines the Unicode character that is used to represent
each of the values 0 to 9 in the final result string: Unicode is
organized so that each set of decimal digits forms a contiguous
block of characters in numerical sequence.]

The following attributes control the interpretation of
characters in the picture string supplied to the format-number
function. In each case the value must be a single character (see
[err:XQST0100]).

[Definition:
digit-sign specifies the character used for the digit-sign
in the picture string; the default value is the number sign
character (#)]

[Definition:
pattern-separator-sign specifies the character used for the
pattern-separator-sign, which separates positive and negative
sub-pictures in a picture string; the default value is the
semi-colon character (;)]

The following attributes specify characters or strings that may
appear in the result of formatting the number:

[Definition:
infinity specifies the string used for the infinity-symbol;
the default value is the string Infinity]

[Definition: NaN specifies
the string used for the NaN-symbol, which is used to represent the
value NaN (not-a-number); the default value is the string NaN]

[Definition:
minus-sign specifies the character used for the
minus-symbol; the default value is the hyphen-minus character (-,
#x2D). The value must be a single character.]

2.1.2 Dynamic
Context

[Definition: The dynamic context of
an expression is defined as information that is available at the
time the expression is evaluated.] If evaluation of an expression
relies on some part of the dynamic context that has not been
assigned a value, a dynamic error is raised [err:XPDY0002].

[Definition:
The first three components of the dynamic context (context item, context
position, and context size) are called the focus of the
expression. ] The focus enables the processor to keep track of
which items are being processed by the expression.

Certain language constructs, notably the path expressionE1/E2 and the predicateE1[E2], create a new
focus for the evaluation of a sub-expression. In these constructs,
E2 is evaluated once for each item in the sequence
that results from evaluating E1. Each time
E2 is evaluated, it is evaluated with a different
focus. The focus for evaluating E2 is referred to
below as the inner focus, while the focus for evaluating
E1 is referred to as the outer focus. The inner
focus exists only while E2 is being evaluated. When
this evaluation is complete, evaluation of the containing
expression continues with its original focus unchanged.

[Definition: The context item is the
item currently being processed. An item is either an atomic value
or a node.] [Definition: When the context item is a node,
it can also be referred to as the context node.] The context
item is returned by an expression consisting of a single dot
(.). When an expression E1/E2 or
E1[E2] is evaluated, each item in the sequence
obtained by evaluating E1 becomes the context item in
the inner focus for an evaluation of E2.

[Definition: The context position
is the position of the context item within the sequence of items
currently being processed.] It changes whenever the context item
changes. When the focus is defined, the value of the context
position is an integer greater than zero. The context position is
returned by the expression fn:position(). When an
expression E1/E2 or E1[E2] is evaluated,
the context position in the inner focus for an evaluation of
E2 is the position of the context item in the sequence
obtained by evaluating E1. The position of the first
item in a sequence is always 1 (one). The context position is
always less than or equal to the context size.

[Definition: The context size is the
number of items in the sequence of items currently being
processed.] Its value is always an integer greater than zero. The
context size is returned by the expression fn:last().
When an expression E1/E2 or E1[E2] is
evaluated, the context size in the inner focus for an evaluation of
E2 is the number of items in the sequence obtained by
evaluating E1.

[Definition: Current dateTime. This
information represents an implementation-dependent point
in time during the processing of a
query, and includes an explicit timezone. It can be
retrieved by the fn:current-dateTime function. If
invoked multiple times during the execution of a query, this function always returns the same
result.]

[Definition: Implicit timezone. This is the
timezone to be used when a date, time, or dateTime value that does
not have a timezone is used in a comparison or arithmetic
operation. The implicit timezone is an implementation-defined value of
type xs:dayTimeDuration. See [XML
Schema] for the range of legal values of a timezone.]

[Definition: Available documents.
This is a mapping of strings onto document nodes. The string
represents the absolute URI of a resource. The document node is the
root of a tree that represents that resource using the data model. The document node
is returned by the fn:doc function when applied to
that URI.] The set of available documents is not limited to the set
of statically known documents, and it may be
empty.

If there are one or more URIs in available documents that map to a
document node D, then the document-uri property of
D must either be absent, or must be one of these
URIs.

Note:

This means that given a document node $N, the
result of fn:doc(fn:document-uri($N)) is $N will
always be True, unless fn:document-uri($N) is an empty
sequence.

[Definition: Available
collections. This is a mapping of strings onto sequences of
nodes. The string represents the absolute URI of a resource. The
sequence of nodes represents the result of the
fn:collection function when that URI is supplied as
the argument. ] The set of available collections is not limited to
the set of statically known collections, and it
may be empty.

For every document node D that is in the target of
a mapping in available collections, or that is
the root of a tree containing such a node, the document-uri
property of D must either be absent, or must be a URI
U such that available documents contains a mapping
from U to D."

Note:

This means that for any document node $N retrieved
using the fn:collection function, either directly or
by navigating to the root of a node that was returned, the result
of fn:doc(fn:document-uri($N)) is $N will always be
True, unless fn:document-uri($N) is an empty sequence.
This implies a requirement for the fn:doc and
fn:collection functions to be consistent in their
effect. If the implementation uses catalogs or user-supplied URI
resolvers to dereference URIs supplied to the fn:doc
function, the implementation of the fn:collection
function must take these mechanisms into account. For example, an
implementation might achieve this by mapping the collection URI to
a set of document URIs, which are then resolved using the same
catalog or URI resolver that is used by the fn:doc
function.

[Definition: Default collection.
This is the sequence of nodes that would result from calling the
fn:collection function with no arguments.] The value
of default collection may be initialized by the
implementation.

2.2
Processing Model

Figure 1 provides a schematic overview of the processing steps
that are discussed in detail below. Some of these steps are
completely outside the domain of XQuery 1.1; in Figure 1, these are
depicted outside the line that represents the boundaries of the
language, an area labeled external processing. The external
processing domain includes generation of an XDM instance that represents the
data to be queried (see 2.2.1 Data Model
Generation), schema import processing (see 2.2.2 Schema Import
Processing) and serialization (see 2.2.4 Serialization). The area
inside the boundaries of the language is known as the query processing domain , which includes the
static analysis and dynamic evaluation phases (see 2.2.3 Expression
Processing). Consistency constraints on the query processing domain are defined in 2.2.5 Consistency
Constraints.

2.2.1 Data Model Generation

Before a query can be processed, its
input data must be represented as an XDM instance. This process occurs
outside the domain of XQuery 1.1, which is why Figure 1 represents
it in the external processing domain. Here are some steps by which
an XML document might be converted to an XDM instance:

A document may be parsed using an XML parser that generates an
XML Information Set (see [XML
Infoset]). The parsed document may then be validated against
one or more schemas. This process, which is described in [XML Schema], results in an abstract information
structure called the Post-Schema Validation Infoset (PSVI).
If a document has no associated schema, its Information Set is
preserved. (See DM1 in Fig. 1.)

The above steps provide an example of how an XDM instance
might be constructed. An XDM instance might also be synthesized
directly from a relational database, or constructed in some other
way (see DM3 in Fig. 1.) XQuery 1.1 is defined in terms of the
data model, but it
does not place any constraints on how XDM instances are
constructed.

The value of an attribute is represented directly within the
attribute node. An attribute node whose type is unknown (such as
might occur in a schemaless document) is given the type annotationxs:untypedAtomic.

The value of an element is represented by the children of the
element node, which may include text nodes and other element nodes.
The type
annotation of an element node indicates how the values in its
child text nodes are to be interpreted. An element that has not
been validated (such as might occur in a schemaless document) is
annotated with the schema type xs:untyped. An element
that has been validated and found to be partially valid is
annotated with the schema type xs:anyType. If an
element node is annotated as xs:untyped, all its
descendant element nodes are also annotated as
xs:untyped. However, if an element node is annotated
as xs:anyType, some of its descendant element nodes
may have a more specific type annotation.

During the static analysis phase, an XQuery
processor may perform type analysis. The effect of type analysis is
to assign a static
type to each expression in the operation tree. [Definition: The static type of an
expression is the best inference that the processor is able to make
statically about the type of the result of the expression.] This
specification does not define the rules for type analysis nor the
static types that are assigned to particular expressions: the only
constraint is that the inferred type must match all possible values
that the expression is capable of returning.

Examples of inferred static types might be:

For the expression concat(a,b) the inferred static
type is xs:string

For the expression $a = $v the inferred static type
is xs:boolean

For the expression $s[exp] the inferred static type
has the same item type as the static type of $s, but a
cardinality that allows the empty sequence even if the static type
of $s does not allow an empty sequence.

The inferred static type of the expression data($x)
(whether written explicitly or inserted into the operation tree in
places where atomization is implicit) depends on the inferred
static type of $x: for example, if $x has
type element(*, xs:integer) then data($x)
has static type xs:integer.

In XQuery 1.0, rules for static type inferencing were published
normatively in [XQuery 1.0 and XPath
2.0 Formal Semantics], but implementations were allowed to
refine these rules to infer a more precise type where possible.
With XQuery 1.1, the rules are entirely implementation-defined.

Every kind of expression also imposes requirements on the type
of its operands. For example, with the expression
substring($a, $b, $c), $a must be of type
xs:string (or something that can be converted to
xs:string by the function calling rules), while
$b and $c must be of type
xs:double.

If the Static Typing Feature is in effect, an XQuery processor
must signal a type error during static analysis if the inferred
static type of an expression is not subsumed by the required type
of the context where the expression is used. For example, the call
of substring above would cause a type error if the inferred static
type of $a is xs:integer; equally, a type
error would be reported during static analysis if the inferred
static type is xs:anyAtomicType.

If the Static Typing Feature is not in effect, a processor may
signal a type error during static analysis only if the inferred
static type of an expression has no overlap (intersection) with the
required type: so for the first argument of substring, the
processor may report an error if the inferred type is
xs:integer, but not if it is
xs:anyAtomicType. Alternatively, if the Static Typing
Feature is not in effect, the processor may defer all type checking
until the dynamic evaluation phase.

2.2.3.2 Dynamic Evaluation Phase

[Definition: The dynamic
evaluation phase is the phase during which the value of an
expression is computed.] It occurs after completion of the
static
analysis phase.

The dynamic evaluation phase depends on the operation
tree of the expression being evaluated (step DQ1), on the input
data (step DQ4), and on the dynamic context (step DQ5), which in turn
draws information from the external environment (step DQ3) and the
static
context (step DQ2). The dynamic evaluation phase may create new
data-model values (step DQ4) and it may extend the dynamic context
(step DQ5)—for example, by binding values to variables.

[Definition: A dynamic type is
associated with each value as it is computed. The dynamic type of a
value may be more specific than the static type of the expression that computed
it (for example, the static type of an expression might be
xs:integer*, denoting a sequence of zero or more
integers, but at evaluation time its value may have the dynamic
type xs:integer, denoting exactly one integer.)]

Even though static typing can catch many type errors before an expression is
executed, it is possible for an expression to raise an error during
evaluation that was not detected by static analysis. For example,
an expression may contain a cast of a string into an integer, which
is statically valid. However, if the actual value of the string at
run time cannot be cast into an integer, a dynamic error will result. Similarly,
an expression may apply an arithmetic operator to a value whose
static type is
xs:untypedAtomic. This is not a static error, but at run
time, if the value cannot be successfully cast to a numeric type, a dynamic error will be
raised.

When the Static Typing Feature is in effect,
it is also possible for static analysis of an expression to raise a
type error, even
though execution of the expression on certain inputs would be
successful. For example, an expression might contain a function
that requires an element as its parameter, and the static analysis
phase might infer the static type of the function parameter to be
an optional element. This case is treated as a type error and inhibits
evaluation, even though the function call would have been
successful for input data in which the optional element is
present.

An XQuery implementation is not required to
provide a serialization interface. For example, an implementation
may only provide a DOM interface (see [Document
Object Model]) or an interface based on an event stream. In
these cases, serialization would be outside of the scope of this
specification.

[XSLT and
XQuery Serialization 1.1] defines a set of serialization
parameters that govern the serialization process. If an XQuery
implementation provides a serialization interface, it may support
(and may expose to users) any of the serialization parameters
listed (with default values) in C.3 Serialization
Parameters.

[Definition: An output
declaration is an option declaration in the predeclared
namespace associated with the output prefix; it is
used to declare an output parameter for serializing the output of
the query.] When the application requests serialization of the
output, the processor may use these parameters to control the way
in which the serialization takes place. Processors may also allow
external mechanisms for specifying serialization parameters, which
may or may not override serialization parameters specified in the
query prolog.

An output declaration may appear only in a
main module; it is a static error [err:XQST0108] if an output declaration appears
in a library
module. It is a static error [err:XQST0110] if the same serialization
parameter is declared more than once. It is a static error [err:XQST0109] if the local
name of an output declaration in the
http://www.w3.org/2009/xquery-serialization namespace
is not one of the serialization parameter names listed in C.3 Serialization
Parameters. The default value for the method parameter is
"xml". An implementation may define additional implementation-defined
serialization parameters in its own namespaces.

A serialization parameter that is not applicable
to the chosen output method must be ignored, except that if its
value is not a valid value for that parameter, the error may be
reported.

A processor that is performing serialization must
report a serialization error if the values of any serialization
parameters (other than any that are ignored under the previous
paragraph) are incorrect.

A processor that is not performing serialization
may report errors if any serialization parameters are incorrect, or
may ignore such parameters.

Specifying serialization parameters in a query
does not by itself demand that the output be serialized. It merely
defines the desired form of the serialized output for use in
situations where the processor has been asked to perform
serialization.

Note:

The data model
permits an element node to have fewer in-scope
namespaces than its parent. Correct serialization of such an
element node would require "undeclaration" of namespaces, which is
a feature of [XML Names 1.1]. An
implementation that does not support [XML
Names 1.1] is permitted to serialize such an element without
"undeclaration" of namespaces, which effectively causes the element
to inherit the in-scope namespaces of its parent.

2.2.5 Consistency Constraints

In order for XQuery 1.1 to be well defined, the input XDM instance, the
static
context, and the dynamic context must be mutually
consistent. The consistency constraints listed below are
prerequisites for correct functioning of an XQuery 1.1
implementation. Enforcement of these consistency constraints is
beyond the scope of this specification. This specification does not
define the result of a query under any
condition in which one or more of these constraints is not
satisfied.

Some of the consistency constraints use the term data model
schema. [Definition: For a given node in an
XDM
instance, the data model schema is defined as the schema
from which the type annotation of that node was
derived.] For a node that was constructed by some process other
than schema validation, the data model schema consists
simply of the schema type definition that is represented by the
type
annotation of the node.

For every node that has a type annotation, if that type
annotation is found in the in-scope schema definitions (ISSD), then its
definition in the ISSD must be equivalent to its definition in the
data
model schema. Furthermore, all types that are derived by
extension from the given type in the data model schema must also be
known by equivalent definitions in the ISSD.

For each variable declared as external: If the
variable declaration includes a declared type, the external
environment must provide a value for the variable that matches the
declared type, using the matching rules in 2.5.4 SequenceType Matching.
If the variable declaration does not include a declared type, the
external environment must provide a type and a matching value,
using the same matching rules.

For a given query, define a participating ISSD as the
in-scope
schema definitions of a module that is used in evaluating the
query. If two participating ISSDs contain a definition for the same
schema type, element name, or attribute name, the definitions must
be equivalent in both ISSDs. Furthermore, if two participating
ISSDs each contain a definition of a schema type T, the
set of types derived by extension from T must be
equivalent in both ISSDs. Also, if two participating ISSDs each
contain a definition of an element name E, the
substitution group headed by E must be equivalent in both
ISSDs.

In the statically known namespaces, the prefix
xml must not be bound to any namespace URI other than
http://www.w3.org/XML/1998/namespace, and no prefix
other than xml may be bound to this namespace URI.

[Definition: A static error is an error
that must be detected during the static analysis phase. A syntax
error is an example of a static error.]

[Definition: A dynamic error is an
error that must be detected during the dynamic evaluation phase and
may be detected during the static analysis phase. Numeric overflow
is an example of a dynamic error. ]

[Definition: A type error may be raised
during the static analysis phase or the dynamic evaluation phase.
During the static analysis phase, a type error occurs when the static type of an
expression does not match the expected type of the context in which
the expression occurs. During the dynamic evaluation phase, a
type error occurs
when the dynamic
type of a value does not match the expected type of the context
in which the value occurs.]

In addition to the errors defined in this specification, an
implementation may raise a dynamic error for a reason beyond the scope
of this specification. For example, limitations may exist on the
maximum numbers or sizes of various objects. Any such limitations,
and the consequences of exceeding them, are implementation-dependent.

2.3.2 Identifying and Reporting
Errors

The errors defined in this specification are identified by
QNames that have the form err:XXYYnnnn, where:

err denotes the namespace for XPath and XQuery
errors, http://www.w3.org/2005/xqt-errors. This
binding of the namespace prefix err is used for
convenience in this document, and is not normative.

XX denotes the language in which the error is
defined, using the following encoding:

XP denotes an error defined by XPath. Such an error
may also occur XQuery since XQuery includes XPath as a subset.

XQ denotes an error defined by XQuery.

YY denotes the error category, using the following
encoding:

ST denotes a static error.

DY denotes a dynamic error.

TY denotes a type error.

nnnn is a unique numeric code.

Note:

The namespace URI for XPath and XQuery errors is not expected to
change from one version of XQuery 1.1 to another. However, the
contents of this namespace may be extended to include additional
error definitions.

The method by which an XQuery 1.1 processor reports error
information to the external environment is implementation-defined.

An error can be represented by a URI reference that is derived
from the error QName as follows: an error with namespace URI
NS and local part LP
can be represented as the URI reference NS#LP . For example, an error
whose QName is err:XPST0017 could be represented as
http://www.w3.org/2005/xqt-errors#XPST0017.

Note:

Along with a code identifying an error, implementations may wish
to return additional information, such as the location of the error
or the processing phase in which it was detected. If an
implementation chooses to do so, then the mechanism that it uses to
return this information is implementation-defined.

2.3.3 Handling Dynamic Errors

Except as noted in this document, if any operand of an
expression raises a dynamic error, the expression also raises a
dynamic
error. If an expression can validly return a value or raise a
dynamic error, the implementation may choose to return the value or
raise the dynamic error. For example, the logical expression
expr1 and expr2 may return the value
false if either operand returns false, or
may raise a dynamic error if either operand raises a dynamic
error.

If more than one operand of an expression raises an error, the
implementation may choose which error is raised by the expression.
For example, in this expression:

($x div $y) + xs:decimal($z)

both the sub-expressions ($x div $y) and
xs:decimal($z) may raise an error. The implementation
may choose which error is raised by the "+"
expression. Once one operand raises an error, the implementation is
not required, but is permitted, to evaluate any other operands.

[Definition: In addition to its identifying
QName, a dynamic error may also carry a descriptive string and one
or more additional values called error values.] An
implementation may provide a mechanism whereby an
application-defined error handler can process error values and
produce diagnostic messages.

A dynamic error can also be raised explicitly by calling the
fn:error function, which only raises an error and
never returns a value. This function is defined in [XQuery and XPath Functions and Operators
1.1]. For example, the following function call raises a dynamic
error, providing a QName that identifies the error, a descriptive
string, and a diagnostic value (assuming that the prefix
app is bound to a namespace containing
application-defined error codes):

fn:error(xs:QName("app:err057"), "Unexpected value", fn:string($v))

2.3.4
Errors and Optimization

Because different implementations may choose to evaluate or
optimize an expression in different ways, certain aspects of the
detection and reporting of dynamic errors are implementation-dependent, as
described in this section.

An implementation is always free to evaluate the operands of an
operator in any order.

In some cases, a processor can determine the result of an
expression without accessing all the data that would be implied by
the formal expression semantics. For example, the formal
description of filter expressions suggests that
$s[1] should be evaluated by examining all the items
in sequence $s, and selecting all those that satisfy
the predicate position()=1. In practice, many
implementations will recognize that they can evaluate this
expression by taking the first item in the sequence and then
exiting. If $s is defined by an expression such as
//book[author eq 'Berners-Lee'], then this strategy
may avoid a complete scan of a large document and may therefore
greatly improve performance. However, a consequence of this
strategy is that a dynamic error or type error that would be
detected if the expression semantics were followed literally might
not be detected at all if the evaluation exits early. In this
example, such an error might occur if there is a book
element in the input data with more than one author
subelement.

The extent to which a processor may optimize its access to data,
at the cost of not detecting errors, is defined by the following
rules.

Consider an expression Q that has an operand
(sub-expression) E. In general the value of E is
a sequence. At an intermediate stage during evaluation of the
sequence, some of its items will be known and others will be
unknown. If, at such an intermediate stage of evaluation, a
processor is able to establish that there are only two possible
outcomes of evaluating Q, namely the value V or
an error, then the processor may deliver the result V
without evaluating further items in the operand E. For
this purpose, two values are considered to represent the same
outcome if their items are pairwise the same, where nodes are the
same if they have the same identity, and values are the same if
they are equal and have exactly the same type.

There is an exception to this rule: If a processor evaluates an
operand E (wholly or in part), then it is required to
establish that the actual value of the operand E does not
violate any constraints on its cardinality. For example, the
expression $e eq 0 results in a type error if the
value of $e contains two or more items. A processor is
not allowed to decide, after evaluating the first item in the value
of $e and finding it equal to zero, that the only
possible outcomes are the value true or a type error
caused by the cardinality violation. It must establish that the
value of $e contains no more than one item.

These rules apply to all the operands of an expression
considered in combination: thus if an expression has two operands
E1 and E2, it may be evaluated using any samples
of the respective sequences that satisfy the above rules.

The rules cascade: if A is an operand of B and
B is an operand of C, then the processor needs to
evaluate only a sufficient sample of B to determine the
value of C, and needs to evaluate only a sufficient sample
of A to determine this sample of B.

The effect of these rules is that the processor is free to stop
examining further items in a sequence as soon as it can establish
that further items would not affect the result except possibly by
causing an error. For example, the processor may return
true as the result of the expression S1 =
S2 as soon as it finds a pair of equal values from the two
sequences.

Another consequence of these rules is that where none of the
items in a sequence contributes to the result of an expression, the
processor is not obliged to evaluate any part of the sequence.
Again, however, the processor cannot dispense with a required
cardinality check: if an empty sequence is not permitted in the
relevant context, then the processor must ensure that the operand
is not an empty sequence.

Examples:

If an implementation can find (for example, by using an index)
that at least one item returned by $expr1 in the
following example has the value 47, it is allowed to
return true as the result of the some
expression, without searching for another item returned by
$expr1 that would raise an error if it were
evaluated.

some $x in $expr1 satisfies $x = 47

In the following example, if an implementation can find (for
example, by using an index) the product element-nodes
that have an id child with the value 47,
it is allowed to return these nodes as the result of the path expression,
without searching for another product node that would
raise an error because it has an id child whose value
is not an integer.

//product[id = 47]

For a variety of reasons, including optimization,
implementations may rewrite expressions into a different form.
There are a number of rules that limit the extent of this
freedom:

Other than the raising or not raising of errors, the result of
evaluating a rewritten expression must conform to the semantics
defined in this specification for the original expression.

Note:

This allows an implementation to return a result in cases where
the original expression would have raised an error, or to raise an
error in cases where the original expression would have returned a
result. The main cases where this is likely to arise in practice
are (a) where a rewrite changes the order of evaluation, such that
a subexpression causing an error is evaluated when the expression
is written one way and is not evaluated when the expression is
written a different way, and (b) where intermediate results of the
evaluation cause overflow or other out-of-range conditions.

Note:

This rule does not mean that the result of the expression will
always be the same in non-error cases as if it had not been
rewritten, because there are many cases where the result of an
expression is to some degree implementation-dependent or
implementation-defined.

Conditional and typeswitch expressions must not raise a dynamic
error in respect of subexpressions occurring in a branch that is
not selected, and must not return the value delivered by a branch
unless that branch is selected. Thus, the following example must
not raise a dynamic error if the document abc.xml does
not exist:

if (doc-available('abc.xml')) then doc('abc.xml') else ()

As stated earlier, an expression must not be rewritten to
dispense with a required cardinality check: for example,
string-length(//title) must raise an error if the
document contains more than one title element.

Expressions must not be rewritten in such a way as to create or
remove static errors. For example, there is a rule that in casting
a string to a QName the operand must be a string literal. This rule
applies to the original expression and not to any rewritten form of
the expression.

Expression rewrite is illustrated by the following examples.

Consider the expression //part[color eq "Red"]. An
implementation might choose to rewrite this expression as
//part[color = "Red"][color eq "Red"]. The
implementation might then process the expression as follows: First
process the "=" predicate by probing an index on parts
by color to quickly find all the parts that have a Red color; then
process the "eq" predicate by checking each of these
parts to make sure it has only a single color. The result would be
as follows:

Parts that have exactly one color that is Red are returned.

If some part has color Red together with some other color, an
error is raised.

The existence of some part that has no color Red but has
multiple non-Red colors does not trigger an error.

The expression in the following example cannot raise a casting
error if it is evaluated exactly as written (i.e., left to right).
Since neither predicate depends on the context position, an
implementation might choose to reorder the predicates to achieve
better performance (for example, by taking advantage of an index).
This reordering could cause the expression to raise an error.

$N[@x castable as xs:date][xs:date(@x) gt xs:date("2000-01-01")]

To avoid unexpected errors caused by expression rewrite, tests
that are designed to prevent dynamic errors should be expressed
using conditional or
typeswitch expressions. For example, the above
expression can be written as follows:

2.4 Concepts

This section explains some concepts that are important to the
processing of XQuery 1.1 expressions.

2.4.1
Document Order

An ordering called document order is defined among all
the nodes accessible during processing of a given query, which may consist of one or more
trees (documents or fragments). Document order is defined in
[XQuery and XPath Data Model (XDM)
1.1], and its definition is repeated here for convenience.
[Definition: The node ordering
that is the reverse of document order is called reverse document
order.]

Document order is a total ordering, although the relative order
of some nodes is implementation-dependent.
[Definition: Informally, document
order is the order in which nodes appear in the XML
serialization of a document.] [Definition: Document order is stable, which
means that the relative order of two nodes will not change during
the processing of a given query, even
if this order is implementation-dependent.]

Within a tree, document order satisfies the following
constraints:

The root node is the first node.

Every node occurs before all of its children and
descendants.

Attribute nodes immediately follow the element node with which
they are associated. The relative order of attribute nodes is
stable but implementation-dependent.

The relative order of siblings is the order in which they occur
in the children property of their parent node.

Children and descendants occur before following siblings.

The relative order of nodes in distinct trees is stable but
implementation-dependent,
subject to the following constraint: If any node in a given tree T1
is before any node in a different tree T2, then all nodes in tree
T1 are before all nodes in tree T2.

2.4.2
Atomization

The semantics of some XQuery 1.1 operators depend on a process
called atomization. Atomization is applied to a
value when the value is used in a context in which a sequence of
atomic values is required. The result of atomization is either a
sequence of atomic values or a type error [err:FOTY0012]. [Definition: Atomization of a sequence
is defined as the result of invoking the fn:data
function on the sequence, as defined in [XQuery and XPath Functions and Operators
1.1].]

The semantics of fn:data are repeated here for
convenience. The result of fn:data is the sequence of
atomic values produced by applying the following rules to each item
in the input sequence:

If the item is an atomic value, it is returned.

If the item is a node, its typed value is returned (err:FOTY0012 is
raised if the node has no typed value.)

The dynamic semantics of fn:boolean are repeated
here for convenience:

If its operand is an empty sequence, fn:boolean
returns false.

If its operand is a sequence whose first item is a node,
fn:boolean returns true.

If its operand is a singleton value of type xs:boolean
or derived from xs:boolean, fn:boolean
returns the value of its operand unchanged.

If its operand is a singleton value of type xs:string,
xs:anyURI, xs:untypedAtomic, or a type
derived from one of these, fn:boolean returns
false if the operand value has zero length; otherwise
it returns true.

If its operand is a singleton value of any numeric type or derived from a numeric type,
fn:boolean returns false if the operand
value is NaN or is numerically equal to zero;
otherwise it returns true.

In all other cases, fn:boolean raises a type error
[err:FORG0006].

Note:

The effective
boolean value of a sequence that contains at least one node and
at least one atomic value may be nondeterministic in regions of a
query where ordering mode is
unordered.

The effective
boolean value of a sequence is computed implicitly during
processing of the following types of expressions:

The definition of effective boolean value is not used when
casting a value to the type xs:boolean, for example in
a cast expression or when passing a value to a
function whose expected parameter is of type
xs:boolean.

2.4.4
Input Sources

XQuery 1.1 has a set of functions that provide access to input
data. These functions are of particular importance because they
provide a way in which an expression can reference a document or a
collection of documents. The input functions are described
informally here; they are defined in [XQuery and XPath Functions and Operators
1.1].

An expression can access input data either by calling one of the
input functions or by referencing some part of the dynamic context
that is initialized by the external environment, such as a
variable
or context
item.

The fn:collection function with one argument takes
a string containing a URI. If that URI is associated with a
collection in available collections,
fn:collection returns the data model representation of
that collection; otherwise it raises a dynamic error (see [XQuery and XPath Functions and Operators
1.1] for details). A collection may be any sequence of nodes.
For example, the expression
fn:collection("http://example.org")//customer
identifies all the customer elements that are
descendants of nodes found in the collection whose URI is
http://example.org.

2.4.5 URI
Literals

In certain places in the XQuery grammar, a statically known
valid URI is required. These places are denoted by the grammatical
symbol URILiteral. For
example, URILiterals are used to specify namespaces and collations,
both of which must be statically known.

Syntactically, a URILiteral is identical to a StringLiteral: a sequence of zero
or more characters enclosed in single or double quotes. However, an
implementation may raise a static error [err:XQST0046] if the value of a URILiteral is of
nonzero length and is not in the lexical space of
xs:anyURI.

The URILiteral is subjected to whitespace normalization as
defined for the xs:anyURI type in [XML Schema]: this means that leading and trailing
whitespace is removed, and any other sequence of whitespace
characters is replaced by a single space (#x20) character.
Whitespace normalization is done after the expansion of character
references, so writing a newline (for example) as
&#xA; does not prevent its being normalized to a
space character.

The URILiteral is not automatically subjected to
percent-encoding or decoding as defined in [RFC3986]. Any process that attempts to resolve the
URI against a base URI, or to dereference the URI, may however
apply percent-encoding or decoding as defined in the relevant
RFCs.

Note:

The xs:anyURI type is designed to anticipate the
introduction of Internationalized Resource Identifiers (IRI's) as
defined in [RFC3987].

The following is an example of a valid URILiteral:

"http://www.w3.org/2005/xpath-functions/collation/codepoint"

2.5 Types

[Definition: A sequence type is a type
that can be expressed using the SequenceType syntax. Sequence
types are used whenever it is necessary to refer to a type in an
XQuery 1.1 expression. The term sequence type suggests that
this syntax is used to describe the type of an XQuery 1.1 value,
which is always a sequence.]

[Definition: A schema type is a type
that is (or could be) defined using the facilities of [XML Schema] (including the built-in types of
[XML Schema]).] A schema type can be used
as a type annotation on an element or attribute node (unless it is
a non-instantiable type such as xs:NOTATION or
xs:anyAtomicType, in which case its derived types can
be so used). Every schema type is either a complex type or a
simple type; simple types are further subdivided into
list types, union types, and atomic types (see
[XML Schema] for definitions and
explanations of these terms.)

[Definition: xs:untyped is used as the
type
annotation of an element node that has not been validated, or
has been validated in skip mode.] No predefined schema
types are derived from xs:untyped.

[Definition: xs:untypedAtomic is
an atomic type that is used to denote untyped atomic data, such as
text that has not been assigned a more specific type.] An attribute
that has been validated in skip mode is represented in
the data model by an
attribute node with the type annotationxs:untypedAtomic. No predefined schema types are
derived from xs:untypedAtomic.

[Definition:
xs:dayTimeDuration is derived by restriction from
xs:duration. The lexical representation of
xs:dayTimeDuration is restricted to contain only day,
hour, minute, and second components.]

[Definition:
xs:yearMonthDuration is derived by restriction from
xs:duration. The lexical representation of
xs:yearMonthDuration is restricted to contain only
year and month components.]

[Definition: xs:anyAtomicType is
an atomic type that includes all atomic values (and no values that
are not atomic). Its base type is xs:anySimpleType
from which all simple types, including atomic, list, and union
types, are derived. All primitive atomic types, such as
xs:decimal and xs:string, have
xs:anyAtomicType as their base type.]

Note:

xs:anyAtomicType will not appear as the type of an
actual value in an XDM instance.

2.5.2 Typed
Value and String Value

Every node has a typed value and a string value.
[Definition: The typed value of a node
is a sequence of atomic values and can be extracted by applying the
fn:data function to the node.] [Definition: The string value of a node
is a string and can be extracted by applying the
fn:string function to the node.] Definitions of
fn:data and fn:string can be found in
[XQuery and XPath Functions and
Operators 1.1].

An implementation may store both the typed value and the string value of a node,
or it may store only one of these and derive the other as needed.
The string value of a node must be a valid lexical representation
of the typed value of the node, but the node is not required to
preserve the string representation from the original source
document. For example, if the typed value of a node is the
xs:integer value 30, its string value
might be "30" or "0030".

As a convenience to the reader, the relationship between
typed value and
string value
for various kinds of nodes is summarized and illustrated by
examples below.

For text and document nodes, the typed value of the node is the
same as its string value, as an instance of the type
xs:untypedAtomic. The string value of a document node
is formed by concatenating the string values of all its descendant
text nodes, in document order.

The typed value of a comment or processing instruction node is
the same as its string value. It is an instance of the type
xs:string.

The typed value of an attribute node with the type annotationxs:anySimpleType or xs:untypedAtomic is
the same as its string value, as an instance of
xs:untypedAtomic. The typed value of an attribute node
with any other type annotation is derived from its string value and
type annotation using the lexical-to-value-space mapping defined in
[XML Schema] Part 2 for the relevant
type.

Example: A1 is an attribute having string value
"3.14E-2" and type annotation xs:double.
The typed value of A1 is the xs:double value whose
lexical representation is 3.14E-2.

Example: A2 is an attribute with type annotation
xs:IDREFS, which is a list datatype whose item type is
the atomic datatype xs:IDREF. Its string value is
"bar baz faz". The typed value of A2 is a sequence of
three atomic values ("bar", "baz",
"faz"), each of type xs:IDREF. The typed
value of a node is never treated as an instance of a named list
type. Instead, if the type annotation of a node is a list type
(such as xs:IDREFS), its typed value is treated as a
sequence of the atomic type from which it is derived (such as
xs:IDREF).

For an element node, the relationship between typed value and
string value depends on the node's type annotation, as follows:

If the type annotation is xs:untyped or
xs:anySimpleType or denotes a complex type with mixed
content (including xs:anyType), then the typed value
of the node is equal to its string value, as an instance of
xs:untypedAtomic. However, if the nilled
property of the node is true, then its typed value is
the empty sequence.

Example: E1 is an element node having type annotation
xs:untyped and string value "1999-05-31".
The typed value of E1 is "1999-05-31", as an instance
of xs:untypedAtomic.

Example: E2 is an element node with the type annotation
formula, which is a complex type with mixed content.
The content of E2 consists of the character "H", a
child element named subscript with string value
"2", and the character "O". The typed
value of E2 is "H2O" as an instance of
xs:untypedAtomic.

If the type annotation denotes a simple type or a complex type
with simple content, then the typed value of the node is derived
from its string value and its type annotation in a way that is
consistent with schema validation. However, if the
nilled property of the node is true, then
its typed value is the empty sequence.

Example: E3 is an element node with the type annotation
cost, which is a complex type that has several
attributes and a simple content type of xs:decimal.
The string value of E3 is "74.95". The typed value of
E3 is 74.95, as an instance of
xs:decimal.

Example: E4 is an element node with the type annotation
hatsizelist, which is a simple type derived from the
atomic type hatsize, which in turn is derived from
xs:integer. The string value of E4 is "7 8
9". The typed value of E4 is a sequence of three values
(7, 8, 9), each of type
hatsize.

Example: E5 is an element node with the type annotation
my:integer-or-string which is a union type with member
types xs:integer and xs:string. The
string value of E5 is "47". The typed value of E5 is
47 as an xs:integer, since
xs:integer is the member type that validated the
content of E5. In general, when the type annotation of a node is a
union type, the typed value of the node will be an instance of one
of the member types of the union.

Note:

If an implementation stores only the string value of a node, and
the type annotation of the node is a union type, the implementation
must be able to deliver the typed value of the node as an instance
of the appropriate member type.

If the type annotation denotes a complex type with empty
content, then the typed value of the node is the empty sequence and
its string value is the zero-length string.

If the type annotation denotes a complex type with element-only
content, then the typed value of the node is undefined. The
fn:data function raises a type error [err:FOTY0012] when applied to such
a node. The string value of such a node is equal to the
concatenated string values of all its text node descendants, in
document order.

Example: E6 is an element node with the type annotation
weather, which is a complex type whose content type
specifies element-only. E6 has two child elements
named temperature and precipitation. The
typed value of E6 is undefined, and the fn:data
function applied to E6 raises an error.

2.5.3 SequenceType Syntax

Whenever it is necessary to refer to a type in an XQuery 1.1
expression, the SequenceType syntax is used.

With the exception of the special type
empty-sequence(), a sequence type consists of an item
type that constrains the type of each item in the sequence, and
a cardinality that constrains the number of items in the
sequence. Apart from the item type item(), which
permits any kind of item, item types divide into node types
(such as element()), atomic types (such as
xs:integer) and function types (such as function() as
item()*).

Item types representing element and attribute nodes may specify
the required type annotations of those nodes, in the
form of a schema
type. Thus the item type element(*, us:address)
denotes any element node whose type annotation is (or is derived
from) the schema type named us:address.

Here are some examples of sequence types that might be used in XQuery
1.1 expressions:

xs:date refers to the built-in atomic schema type
named xs:date

attribute()? refers to an optional attribute
node

element() refers to any element node

element(po:shipto, po:address) refers to an element
node that has the name po:shipto and has the type
annotation po:address (or a schema type derived from
po:address)

element(*, po:address) refers to an element node of
any name that has the type annotation po:address (or a
type derived from po:address)

element(customer) refers to an element node named
customer with any type annotation

schema-element(customer) refers to an element node
whose name is customer (or is in the substitution
group headed by customer) and whose type annotation
matches the schema type declared for a customer
element in the in-scope element declarations

node()* refers to a sequence of zero or more nodes
of any kind

item()+ refers to a sequence of one or more nodes
or atomic values

function(*) refers to any function
itemDM11, regardless of arity or
type

function(node()) as xs:string* refers to a function
itemDM11 that takes a single argument
whose value is a single node, and returns a sequence of zero or
more xs:string values

(function(node()) as xs:string)* refers to a
sequence of zero or more function
itemsDM11, each of which takes a
single argument whose value is a single node, and returns as its
result a single xs:string value

2.5.4 SequenceType Matching

[Definition: During evaluation
of an expression, it is sometimes necessary to determine whether a
value with a known dynamic type "matches" an expected sequence type. This
process is known as SequenceType matching.] For example, an
instance of expression returns true if
the dynamic
type of a given value matches a given sequence type, or false
if it does not.

Some of the rules for SequenceType matching require
determining whether a given schema type encountered as a type
annotation in an instance document is the same as or derived from
an expected schema type. This determination is done by reference to
a schema S (that is, a set of schema components). This
schema S is the union of:

the in-scope schema definitions in the static context of the
query module

potentially, the schema used for validating the instance
document; whether a processor adds this schema to S is
implementation-defined.

potentially, further schema components that have been made
available to the processor in an implementation-defined
way.

A type error [err:XPTY0004] may be raised if this union does
not constitute a valid schema (for example, if there are conflicts
between types present in the static context and types used
dynamically for validating instances.)

Whether the schema used to validate the instance document is in
S is implementation-defined. Whether the implementation
provides further schema components in S is also
implementation-defined.

[Definition: The use of a value
whose dynamic
type is derived from an expected type is known as subtype
substitution.] Subtype substitution does not change the actual
type of a value. For example, if an xs:integer value
is used where an xs:decimal value is expected, the
value retains its type as xs:integer.

The definition of SequenceType matching relies on a
pseudo-function named derives-from(AT,
ET), which takes an actual simple
or complex schema type AT and an expected simple or
complex schema type ET , and either returns a
boolean value or raises a type error [err:XPTY0004]. This function is defined as
follows:

derives-from(AT, ET) raises a type error [err:XPTY0004] if either
AT or ET is not present in S

derives-from(AT, ET) returns true AT and ET are both
present in S, and if one or more of the following three
conditions is true:

AT is the same type as ET

AT is derived by restriction or extension from
ET

Note:

Some members of the XML Query Working Group believe that
matching types derived by restriction should be required, but
extension from ET should be implementation-defined, others
believe matching types derived by extension from ET should
be required of all implementations.

Some implementations that do static analysis may do
optimizations that would be invalidated by allowing dynamically
encountered types derived by extension from ET.

If these implementations do not add such types to S,
they will not encounter such types. Some implementers argue that
they would like the freedom to use dynamic schema information in
queries, but still want to be able to optimize statically. Some
Working Group members suggest that it is a clearer model to either
use all schema information from dynamically encountered schemas,
including derivation by extension, or not place it in
S.

The XML Query Working Group has not reached consensus on this
question, and we welcome feedback.

S contains some schema type IT such that
derives-from(IT, ET)
and derives-from(AT, IT) are true.

Otherwise, derives-from(AT, ET) returns false

The rules for SequenceType matching are given
below, with examples (the examples are for purposes of
illustration, and do not cover all possible cases).

2.5.4.1
Matching a SequenceType and a Value

The sequence
typeempty-sequence() matches a value that is the
empty sequence.

Example: The AtomicTypexs:decimal matches the value 12.34 (a
decimal literal). xs:decimal also matches a value
whose type is shoesize, if shoesize is an
atomic type derived by restriction from
xs:decimal.

Note:

The names of non-atomic types such as xs:IDREFS are
not accepted in this context, but can often be replaced by an
atomic type with an occurrence indicator, such as
xs:IDREF+.

processing-instruction(N)
matches any processing-instruction node whose PITarget is equal to
fn:normalize-space(N). If
fn:normalize-space(N) is not in the lexical space of
NCName, a type error is raised [err:XPTY0004]

element() and element(*) match any
single element node, regardless of its name or type annotation.

element(ElementName) matches
any element node whose name is ElementName, regardless of its type
annotation or nilled property.

Example: element(person) matches any element node
whose name is person.

element(ElementName,TypeName) matches an
element node whose name is ElementName if
derives-from(AT, TypeName) is
true, where AT is the type annotation of the
element node, and the nilled property of the node is
false.

Example: element(person, surgeon) matches a
non-nilled element node whose name is person and whose
type annotation is surgeon (or is derived from
surgeon).

element(ElementName, TypeName?) matches an
element node whose name is ElementName if
derives-from(AT, TypeName) is
true, where AT is the type annotation of the
element node. The nilled property of the node may be
either true or false.

Example: element(person, surgeon?) matches a nilled
or non-nilled element node whose name is person and
whose type annotation is surgeon (or is derived from
surgeon).

element(*,TypeName) matches an
element node regardless of its name, if derives-from(AT, TypeName) is true, where AT is the type
annotation of the element node, and the nilled
property of the node is false.

element(*,TypeName?) matches an
element node regardless of its name, if derives-from(AT, TypeName) is true, where AT is the type
annotation of the element node. The nilled property of
the node may be either true or false.

Example: The SchemaElementTestschema-element(customer) matches a candidate element
node if customer is a top-level element declaration in
the in-scope element declarations, the name of the
candidate node is customer or is in a substitution
group headed by customer, the type annotation of
the candidate node is the same as or derived from the schema type
declared for the customer element, and either the
candidate node is not nilled or customer
is declared to be nillable.

Example: The SchemaAttributeTestschema-attribute(color) matches a candidate attribute
node if color is a top-level attribute declaration in
the in-scope attribute declarations, the name of the
candidate node is color, and the type annotation of
the candidate node is the same as or derived from the schema type
declared for the color attribute.

2.5.5 SequenceType Subtype
Relationships

Given two sequence types, it is possible to determine
if one is a subtype of the other. [Definition: A sequence typeA is a subtype of a sequence type
B if and only if, for every value V, if
V matches A according to the rules of
SequenceType matching, then
V also matches B.] The subtype
relationship can be computed using the subtype(A, B),
subtype-itemtype(Ai, Bi), and derives-from(AT,
ET) judgements.

2.5.5.1 The SequenceType Subtype
Judgement

The judgement subtype(A, B) determines if the
sequence typeA is a subtype of the sequence type B.
A can either be empty-sequence() or an
ItemType, Ai,
possibly followed by an occurrence indicator. Similarly
B can either be empty-sequence() or an
ItemType, Bi,
possibly followed by an occurrence indicator. The result of the
subtype(A, B) judgement can be determined from the
table below, which makes use of the auxiliary judgement
subtype-itemtype(Ai, Bi) defined in 2.5.5.2 The ItemType Subtype
Judgement.

Bi is element(*, Bt), Ai
is either element(*, At), or element(N,
At) for any name N, and derives-from(At, Bt)
returns true.

Bi is element(*, Bt?), Ai
is either element(*, At), element(*,
At?), element(N, At), or element(N,
At?) for any name N, and derives-from(At, Bt)
returns true.

Bi is schema-element(Bn),
Ai is schema-element(An), and either the
expanded QName An equals the expanded QName
Bn or the element declaration named An is
in the substitution group of the element declaration named
Bn.

3
Expressions

This section discusses each of the basic kinds of expression.
Each kind of expression has a name such as PathExpr,
which is introduced on the left side of the grammar production that
defines the expression. Since XQuery 1.1 is a composable language,
each kind of expression is defined in terms of other expressions
whose operators have a higher precedence. In this way, the
precedence of operators is represented explicitly in the
grammar.

The order in which expressions are discussed in this document
does not reflect the order of operator precedence. In general, this
document introduces the simplest kinds of expressions first,
followed by more complex expressions. For the complete grammar, see
Appendix [A XQuery 1.1 Grammar].

[Definition: A query consists of one or more
modules.] If a query is
executable, one of its modules has a Query Body containing an expression whose value
is the result of the query. An expression is represented in the
XQuery grammar by the symbol Expr.

The XQuery 1.1 operator that has lowest precedence is the
comma
operator, which is used to combine two operands to form a
sequence. As shown in the grammar, a general expression (Expr) can consist of multiple ExprSingle operands, separated by
commas. The name ExprSingle
denotes an expression that does not contain a top-level comma operator
(despite its name, an ExprSingle may evaluate to a
sequence containing more than one item.)

The symbol ExprSingle is
used in various places in the grammar where an expression is not
allowed to contain a top-level comma. For example, each of the
arguments of a function call must be an ExprSingle, because commas are used
to separate the arguments of a function call.

3.1 Primary Expressions

[Definition: Primary expressions
are the basic primitives of the language. They include literals,
variable references, context item expressions, constructors, and function calls. A primary
expression may also be created by enclosing any expression in
parentheses, which is sometimes helpful in controlling the
precedence of operators.] Constructors are
described in 3.7
Constructors.

The value of a numeric literal containing no
"." and no e or E character
is an atomic value of type xs:integer. The value of a
numeric literal containing "." but no e
or E character is an atomic value of type
xs:decimal. The value of a numeric literal containing
an e or E character is an atomic value of
type xs:double. The value of the numeric literal is
determined by casting it to the appropriate type according to the
rules for casting from xs:untypedAtomic to a numeric
type as specified in Section
17.1.1 Casting from xs:string and
xs:untypedAtomicFO.

The value of a string literal is an atomic value whose
type is xs:string and whose value is the string
denoted by the characters between the delimiting apostrophes or
quotation marks. If the literal is delimited by apostrophes, two
adjacent apostrophes within the literal are interpreted as a single
apostrophe. Similarly, if the literal is delimited by quotation
marks, two adjacent quotation marks within the literal are
interpreted as one quotation mark.

A string literal may contain a predefined
entity reference. [Definition: A predefined
entity reference is a short sequence of characters, beginning
with an ampersand, that represents a single character that might
otherwise have syntactic significance.] Each predefined entity
reference is replaced by the character it represents when the
string literal is processed. The predefined entity references
recognized by XQuery are as follows:

Entity Reference

Character Represented

&lt;

<

&gt;

>

&amp;

&

&quot;

"

&apos;

'

A string literal may also contain a character
reference. [Definition: A character
reference is an XML-style reference to a [Unicode] character, identified by its decimal or
hexadecimal codepoint.] For example, the Euro symbol (€) can be
represented by the character reference &#8364;.
Character references are normatively defined in Section 4.1 of the
XML specification (it is implementation-defined whether the
rules in [XML 1.0] or [XML
1.1] apply.) A static error [err:XQST0090] is raised if a character reference
does not identify a valid character in the version of XML that is
in use.

"He said, ""I don't like it.""" denotes a string
containing two quotation marks and one apostrophe.

"Ben &amp; Jerry&apos;s" denotes the
xs:string value "Ben & Jerry's".

"&#8364;99.50" denotes the
xs:string value "€99.50".

The xs:boolean values true and
false can be represented by calls to the built-in
functionsfn:true() and fn:false(),
respectively.

Values of other atomic types can be constructed by calling the
constructor function for the given
type. The constructor functions for XML Schema built-in types are
defined in [XQuery and XPath
Functions and Operators 1.1]. In general, the name of a
constructor function for a given type is the same as the name of
the type (including its namespace). For example:

3.1.2 Variable
References

[Definition: A variable reference
is a QName preceded by a $-sign.] Two variable references are
equivalent if their local names are the same and their namespace
prefixes are bound to the same namespace URI in the statically known namespaces. An
unprefixed variable reference is in no namespace.

Every variable reference must match a name in the in-scope
variables, which include variables from the following
sources:

A variable may be bound by an XQuery 1.1 expression.
The kinds of expressions that can bind
variables are FLWOR expressions (3.8 FLWOR Expressions),
quantified expressions (3.12 Quantified
Expressions), and typeswitch expressions
(3.14.2 Typeswitch). Function
calls also bind values to the formal parameters of functions before
executing the function body.

Every variable binding has a static scope. The scope defines
where references to the variable can validly occur. It is a
static error
[err:XPST0008] to
reference a variable that is not in scope. If a variable is bound
in the static
context for an expression, that variable is in scope for the
entire expression.

A reference to a variable that was declared
external, but was not bound to a value by the external
environment, raises a dynamic error [err:XPDY0002].

If a variable reference matches two or more variable bindings
that are in scope, then the reference is taken as referring to the
inner binding, that is, the one whose scope is smaller. At
evaluation time, the value of a variable reference is the value of
the expression to which the relevant variable is bound. The scope
of a variable binding is defined separately for each kind of
expression that can bind variables.

3.1.3 Parenthesized Expressions

Parentheses may be used to enforce a particular evaluation order
in expressions that contain multiple operators. For example, the
expression (2 + 4) * 5 evaluates to thirty, since the
parenthesized expression (2 + 4) is evaluated first
and its result is multiplied by five. Without parentheses, the
expression 2 + 4 * 5 evaluates to twenty-two, because
the multiplication operator has higher precedence than the addition
operator.

3.1.4 Context Item Expression

[130]

ContextItemExpr

::=

"."

A context item expression evaluates to the context item, which may
be either a node (as in the expression
fn:doc("bib.xml")/books/book[fn:count(./author)>1])
or an atomic value (as in the expression (1 to 100)[. mod 5
eq 0]).

A function call consists of a QName followed by a
parenthesized list of zero or more expressions, called
arguments. If the QName in the function call has no
namespace prefix, it is considered to be in the default function
namespace.

Argument expressions are evaluated, producing argument values.
The order of argument evaluation is implementation-dependent and a
function need not evaluate an argument if the function can evaluate
its body without evaluating that argument.

If the function is a built-in function, it is evaluated using
the converted argument values. The result is either an instance of
the function's declared return type or a dynamic error. Errors
raised by built-in functions are defined in [XQuery and XPath Functions and Operators
1.1].

If the function is a user-declared function that has a body, the
converted argument values are bound to the formal parameters of the
function, and the function body is evaluated. The value returned by
the function body is then converted to the declared return type of
the function by applying the function conversion rules.

When a converted argument value is bound to a function
parameter, the argument value retains its most specific dynamic type, even
though this type may be derived from the type of the formal
parameter. For example, a function with a parameter $p
of type xs:decimal can be invoked with an argument of
type xs:integer, which is derived from
xs:decimal. During the processing of this function
invocation, the dynamic type of $p inside the
body of the function is considered to be xs:integer.
Similarly, the value returned by a function retains its most
specific type, which may be derived from the declared return type
of the function. For example, a function that has a declared return
type of xs:decimal may in fact return a value of
dynamic type xs:integer.

During evaluation of a function body, the static context and
dynamic
context for expression evaluation are defined by the module in which the function is
declared, which is not necessarily the same as the module in which the function is
called. For example, the variables in scope while evaluating a
function body are defined by in-scope variables of the module that
declares the function rather than the module in which the function
is called. During evaluation of a function body, the focus (context item, context position,
and context size) is undefined, except where it is defined by some
expression inside the function body.

[Definition: The function conversion
rules are used to convert an argument value or a return value to its expected type; that is, to
the declared type of the function parameter or
return. ] The expected type is expressed as a sequence type. The
function conversion rules are applied to a given value as
follows:

If the expected type is a sequence of an atomic type (possibly
with an occurrence indicator *, +, or
?), the following conversions are applied:

Atomization is
applied to the given value, resulting in a sequence of atomic
values.

Each item in the atomic sequence that is of type
xs:untypedAtomic is cast to the expected atomic type.
For built-in functions where the expected
type is specified as numeric, arguments of type
xs:untypedAtomic are cast to
xs:double.

For each numeric item
in the atomic sequence that can be promoted to the expected atomic type using
numeric promotion as described in B.1 Type
Promotion, the promotion is done.

For each item of type xs:anyURI in the atomic
sequence that can be promoted to the expected atomic type using
URI promotion as described in B.1 Type
Promotion, the promotion is done.

If, after the above conversions, the resulting value does not
match the expected type according to the rules for SequenceType Matching, a type error is raised
[err:XPTY0004].
If the function call takes place in a
module other than the
module in which the
function is defined, this rule must be satisfied in both the module
where the function is called and the module where the function is
defined (the test is repeated because the two modules may have
different in-scope schema definitions.) Note that the
rules for SequenceType Matching permit a
value of a derived type to be substituted for a value of its base
type.

Since the arguments of a function call are separated by commas,
any argument expression that contains a top-level comma operator must
be enclosed in parentheses. Here are some illustrative examples of
function calls:

my:three-argument-function(1, 2, 3) denotes a
function call with three arguments.

my:two-argument-function((1, 2), 3) denotes a
function call with two arguments, the first of which is a sequence
of two values.

my:two-argument-function(1, ()) denotes a function
call with two arguments, the second of which is an empty
sequence.

my:one-argument-function((1, 2, 3)) denotes a
function call with one argument that is a sequence of three
values.

my:one-argument-function(( )) denotes a function
call with one argument that is an empty sequence.

Function item coercion is only defined to operate on function
itemsDM11. Given a function item,
$function, function item coercion returns a new
function item with the following properties (as defined in Section
2.7 Function ItemsDM11):

An empty set of variable values.

The name of $function.

A function
signatureDM11 equal to the expected
type for the function argument or return type.

A new function, whose result is calculated by invoking
$function with the arguments that were specified at
the new function's invocation.

If the result of invoking the new function item would
necessarily result in a type error, that error may be raised during
function coercion. It is implementation dependent whether this
happens or not.

These rules have the following consequences:

SequenceType matching of the function item's arguments and
result are delayed until that function item is invoked.

The function conversion rules applied to the function item's
arguments and result are defined by the SequenceType it has most
recently been coerced to. Additional function conversion rules
could apply when the wrapped function item is invoked.

If an implementation has static type information about a
function item, that can be used to type check the function item's
argument and return types during static analysis.

The function item $f has a static type of
function(item()*) as item()*. When the
local:filter() function is called, the following
occurs to the function item:

The function conversion rules result in applying function
coercion to $function, wrapping $f in a new inline
function ($p) with the signature function(xs:string) as
xs:boolean.

$p is matched against the SequenceType of
function(xs:string) as xs:boolean, and succeeds.

When $p is invoked inside the predicate, function conversion and
SequenceType matching rules are applied to the context item
argument, resulting in a xs:string value or a type
error.

$f is invoked with the xs:string, which returns a
xs:boolean.

$p applies function conversion rules to the result sequence from
$f, which already matches its declared return type of
xs:boolean.

The xs:boolean is returned as the result of $p.

Note:

Although the semantics of function item coercion are specified
in terms of wrapping the function items, static typing will often
be able to reduce the number of places where this is actually
necessary.

3.1.6 Literal Function Items

[Definition: A literal function
item creates a function
itemDM11 that represents a named function.]
[Definition: A named function is a
function defined in the static context for the query. To uniquely
identify a particular named function, both its name as a QName and
its arity are required.]

If the QName in the literal function item has no namespace
prefix, it is considered to be in the default function
namespace.

If the expanded QName and arity in a literal function item do
not match the name and arity of a function signature in the static
context, a static error is raised [err:XPST0017].

The result of a literal function item is a single function item
with the following properties (as defined in Section
2.7 Function ItemsDM11):

An empty set of variable values.

The name specified in the literal function item.

The function
signatureDM11 of the function from
the static context that matches the name and arity given.

The function from the static context that matches the name and
arity given.

Certain functions in the [XQuery
and XPath Functions and Operators 1.1] specification are
defined to be polymorphic. These are denoted as accepting
parameters of "numeric" type, or returning "numeric" type. Here
"numeric" is a pseudonym for the four primitive numeric types
xs:decimal, xs:integer, xs:float, and xs:double. The functions in
question are:

fn:abs()

fn:ceiling()

fn:floor()

fn:round()

fn:round-half-to-even()

For the purposes of literal function items, these functions are
regarded as taking arguments and producing results of type
xs:anyAtomicType, with a type error raised at runtime if the
argument value provided is not of the correct numeric type.

Note:

The above way of modeling polymorphic functions is semantically
backwards compatible with XQuery 1.0. An implementation that
supports static typing can choose to model the types of these
functions more accurately if desired.

The following are examples of some literal function item
expressions:

fn:abs#1 references the fn:abs function which takes
a single argument.

3.1.7 Inline
Functions

[Definition: An inline function
expression creates a function
itemDM11 that represents an anonymous
function defined directly in the inline function expression
itself.] An inline function specifies the names and SequenceTypes
of the parameters to the function, the SequenceType of the result,
and the body of the function.

If a function parameter is declared using a name but no type,
its default type is item()*. If the result type is omitted from a
function declaration, its default result type is item()*.

The parameters of a function declaration are considered to be
variables whose scope is the function body. It is a static error
[err:XQST0039] for
a function declaration to have more than one parameter with the
same name.

The static context for the function body is inherited from the
location of the inline function expression, with the exception of
the static type of the context item which is initially
undefined.

The variables in scope for the function body include all
variables representing the function parameters, as well as all
variables that are in scope for the inline function expression.

Note:

Function parameter names can mask variables that would otherwise
be in scope for the function body.

The result of an inline function is a single function item with
the following properties (as defined in Section
2.7 Function ItemsDM11):

The set of variable values for any variables referenced by the
inline function's body.

3.1.8
Dynamic Function Invocation

[Definition: A dynamic function
invocationinvokesDM11
a function
itemDM11, calling the function it
represents.] A dynamic function invocation consists of an
expression that returns the function item and a parenthesized list
of zero or more arguments.

If the function item expression does not return a sequence
consisting of a single function item with the same arity as the
number of specified arguments, a type error is raised [err:XPTY0004].

A dynamic function invocation is evaluated as follows:

Argument values are calculated for the function item using rules
1 and 2 for evaluation of a function call as defined in 3.1.5 Function Calls.

The set of variable values from the function item's closure are
added to the dynamic context with a scope of the invocation of the
function.

The function from the function item is evaluated using the
argument values according to rules 3 -
5 for evaluation of a function call as defined in 3.1.5 Function Calls.

Note:

These rules are derived from the rules for function calls
defined in 3.1.5 Function
Calls except for the addition of a rule to deal with the
use of the variable values from the closure.

The following are examples of some dynamic function
invocations:

This example invokes the function item contained in $f, passing
the arguments 2 and 3:

$f(2, 3)

This example fetches the second item from sequence $f, treats it
as a function item and invokes it, passing a xs:string
argument:

$f[2]("Hi there")

This example invokes the function item $f passing no arguments,
and filters the result with a positional predicate:

$f()[2]

3.2
Path Expressions

[Definition: A path expression can
be used to locate nodes within trees. A path expression consists of
a series of one or more steps,
separated by "/" or "//", and optionally
beginning with "/" or "//".] An initial
"/" or "//" is an abbreviation for one or
more initial steps that are implicitly added to the beginning of
the path expression, as described below.

A path expression consisting of a single step is evaluated as
described in 3.2.1 Steps.

A "/" at the beginning of a path expression is an
abbreviation for the initial step
(fn:root(self::node()) treat as
document-node())/ (however, if the "/"
is the entire path expression, the trailing "/" is
omitted from the expansion.) The effect of this initial step is to
begin the path at the root node of the tree that contains the
context node. If the context item is not a node, a type error is raised
[err:XPTY0020]. At
evaluation time, if the root node above the context node is not a
document node, a dynamic error is raised [err:XPDY0050].

A "//" at the beginning of a path expression is an
abbreviation for the initial steps
(fn:root(self::node()) treat as
document-node())/descendant-or-self::node()/
(however, "//" by itself is not a valid path
expression [err:XPST0003].) The effect of these initial
steps is to establish an initial node sequence that contains the
root of the tree in which the context node is found, plus all nodes
descended from this root. This node sequence is used as the input
to subsequent steps in the path expression. If the context item is
not a node, a type
error is raised [err:XPTY0020]. At evaluation time, if the root
node above the context node is not a document node, a dynamic error is
raised [err:XPDY0050].

Note:

The descendants of a node do not include attribute nodes .

Each non-initial occurrence of "//" in a path
expression is expanded as described in 3.2.4
Abbreviated Syntax, leaving a sequence of steps separated
by "/". This sequence of steps is then evaluated from
left to right. Each operation E1/E2 is evaluated as
follows: Expression E1 is evaluated, and if the result
is not a (possibly empty) sequence of nodes, a type error is raised
[err:XPTY0019].
Each node resulting from the evaluation of E1 then
serves in turn to provide an inner focus for an evaluation
of E2, as described in 2.1.2 Dynamic Context. The sequences
resulting from all the evaluations of E2 are combined
as follows:

If every evaluation of E2 returns a (possibly
empty) sequence of nodes, these sequences are combined, and
duplicate nodes are eliminated based on node identity. If ordering mode is ordered, the
resulting node sequence is returned in document order; otherwise it is
returned in implementation-dependent
order.

If every evaluation of E2 returns a (possibly
empty) sequence of non-nodes, these sequences are concatenated and
returned. If ordering mode is ordered, the
returned sequence preserves the orderings within and among the
subsequences generated by the evaluations of E2;
otherwise the order of the returned sequence is implementation-dependent.

If the multiple evaluations of E2 return at least
one node and at least one non-node, a type error is raised [err:XPTY0018].

Note:

Since each step in a path provides context nodes for the
following step, in effect, only the last step in a path is allowed
to return a sequence of non-nodes.

As an example of a path expression,
child::div1/child::para selects the para
element children of the div1 element children of the
context node, or, in other words, the para element
grandchildren of the context node that have div1
parents.

Note:

The "/" character can be used
either as a complete path expression or as the beginning of a
longer path expression such as "/*". Also,
"*" is both the multiply operator and a wildcard in
path expressions. This can cause parsing difficulties when
"/" appears on the left hand side of "*".
This is resolved using the leading-lone-slash constraint.
For example, "/*" and "/ *" are valid
path expressions containing wildcards, but "/*5" and
"/ * 5" raise syntax errors. Parentheses must be used
when "/" is used on the left hand side of an operator,
as in "(/) * 5". Similarly, "4 + / * 5"
raises a syntax error, but "4 + (/) * 5" is a valid
expression. The expression "4 + /" is also valid,
because / does not occur on the left hand side of the
operator.

[Definition: An axis step returns a
sequence of nodes that are reachable from the context node via a
specified axis. Such a step has two parts: an axis, which
defines the "direction of movement" for the step, and a node test, which selects nodes
based on their kind, name, and/or type annotation.] If the context item is
a node, an axis step returns a sequence of zero or more nodes;
otherwise, a type
error is raised [err:XPTY0020]. If ordering mode is
ordered, the resulting node sequence is returned in
document
order; otherwise it is returned in implementation-dependent
order. An axis step may be either a forward step or a
reverse step, followed by zero or more predicates.

In the abbreviated syntax for a step, the axis can be
omitted and other shorthand notations can be used as described in
3.2.4 Abbreviated Syntax.

The unabbreviated syntax for an axis step consists of the axis
name and node test separated by a double colon. The result of the
step consists of the nodes reachable from the context node via the
specified axis that have the node kind, name, and/or type annotation
specified by the node test. For example, the step
child::para selects the para element
children of the context node: child is the name of the
axis, and para is the name of the element nodes to be
selected on this axis. The available axes are described in 3.2.1.1 Axes. The available node tests are
described in 3.2.1.2 Node Tests.
Examples of steps are provided in 3.2.3
Unabbreviated Syntax and 3.2.4
Abbreviated Syntax.

Only document nodes and element nodes have children. If the
context node is any other kind of node, or if the context node is
an empty document or element node, then the child axis is an empty
sequence. The children of a document node or element node may be
element, processing instruction, comment, or text nodes. Attribute
and document nodes can never appear as children.

the descendant axis is defined as the transitive
closure of the child axis; it contains the descendants of the
context node (the children, the children of the children, and so
on)

the parent axis contains the sequence returned by
the dm:parent accessor in [XQuery and XPath Data Model (XDM) 1.1],
which returns the parent of the context node, or an empty sequence
if the context node has no parent

Note:

An attribute node may have an element node as its parent, even
though the attribute node is not a child of the element node.

the ancestor axis is defined as the transitive
closure of the parent axis; it contains the ancestors of the
context node (the parent, the parent of the parent, and so on)

Note:

The ancestor axis includes the root node of the tree in which
the context node is found, unless the context node is the root
node.

the following-sibling axis contains the context
node's following siblings, those children of the context node's
parent that occur after the context node in document order; if
the context node is an attribute node, the
following-sibling axis is empty

the preceding-sibling axis contains the context
node's preceding siblings, those children of the context node's
parent that occur before the context node in document order; if
the context node is an attribute node, the
preceding-sibling axis is empty

the following axis contains all nodes that are
descendants of the root of the tree in which the context node is
found, are not descendants of the context node, and occur after the
context node in document order

the preceding axis contains all nodes that are
descendants of the root of the tree in which the context node is
found, are not ancestors of the context node, and occur before the
context node in document order

the attribute axis contains the attributes of the
context node, which are the nodes returned by the
dm:attributes accessor in [XQuery and XPath Data Model (XDM) 1.1];
the axis will be empty unless the context node is an element

the self axis contains just the context node
itself

the descendant-or-self axis contains the context
node and the descendants of the context node

the ancestor-or-self axis contains the context node
and the ancestors of the context node; thus, the ancestor-or-self
axis will always include the root node

Axes can be categorized as forward axes and reverse
axes. An axis that only ever contains the context node or nodes
that are after the context node in document order is a forward axis. An axis
that only ever contains the context node or nodes that are before
the context node in document order is a reverse axis.

The parent, ancestor,
ancestor-or-self, preceding, and
preceding-sibling axes are reverse axes; all other
axes are forward axes. The ancestor,
descendant, following,
preceding and self axes partition a
document (ignoring attribute nodes): they do not overlap and
together they contain all the nodes in the document.

[Definition: Every axis has a
principal node kind. If an axis can contain elements, then
the principal node kind is element; otherwise, it is the kind of
nodes that the axis can contain.] Thus:

For the attribute axis, the principal node kind is
attribute.

For all other axes, the principal node kind is element.

3.2.1.2 Node
Tests

[Definition: A node test is a condition
that must be true for each node selected by a step.] The condition may be based on the kind of the
node (element, attribute, text, document, comment, or processing
instruction), the name of the node, or (in the case of element,
attribute, and document nodes), the type annotation of the node.

[Definition: A node test that consists only of a
QName or a Wildcard is called a name test.] A name test is
true if and only if the kind of the node is the principal node
kind for the step axis and the expanded QName of the node is equal (as
defined by the eq operator) to the expanded QName
specified by the name test. For example, child::para
selects the para element children of the context node;
if the context node has no para children, it selects
an empty set of nodes. attribute::abc:href selects the
attribute of the context node with the QName abc:href;
if the context node has no such attribute, it selects an empty set
of nodes.

A name test is not satisfied by an element node whose name does
not match the expanded QName of the name test, even if
it is in a substitution group whose head is the
named element.

A node test * is true for any node of the principal node
kind of the step axis. For example, child::* will
select all element children of the context node, and
attribute::* will select all attributes of the context
node.

A node test can also have the form *:NCName. In
this case, the node test is true for any node of the principal node
kind of the step axis whose local name matches the given
NCName, regardless of its namespace or lack of a namespace.

[Definition: An alternative form of a node test
called a kind test can select nodes based on their kind,
name, and type annotation.] The syntax and
semantics of a kind test are described in 2.5.3 SequenceType Syntax and
2.5.4 SequenceType
Matching. When a kind test is used in a node test, only those nodes on
the designated axis that match the kind test are selected. Shown
below are several examples of kind tests that might be used in path
expressions:

node() matches any node.

text() matches any text node.

comment() matches any comment node.

namespace-node() matches any namespace node.

element() matches any element node.

schema-element(person) matches any element node
whose name is person (or is in the substitution
group headed by person), and whose type annotation
is the same as (or is derived from) the declared type of the
person element in the in-scope
element declarations.

element(person) matches any element node whose name
is person, regardless of its type annotation.

element(person, surgeon) matches any non-nilled
element node whose name is person, and whose type
annotation is surgeon or is derived from
surgeon.

attribute(price) matches any attribute whose name
is price, regardless of its type annotation.

attribute(*, xs:decimal) matches any attribute
whose type annotation is xs:decimal (or is derived
from xs:decimal), regardless of its name.

document-node() matches any document node.

document-node(element(book)) matches any document
node whose content consists of a single element node that satisfies
the kind testelement(book), interleaved with zero or more comments
and processing instructions.

3.2.2
Predicates

[Definition: A predicate consists of an
expression, called a predicate expression, enclosed in
square brackets. A predicate serves to filter a sequence, retaining
some items and discarding others.] In the case of multiple adjacent
predicates, the predicates are applied from left to right, and the
result of applying each predicate serves as the input sequence for
the following predicate.

For each item in the input sequence, the predicate expression is
evaluated using an inner focus, defined as follows: The
context item is the item currently being tested against the
predicate. The context size is the number of items in the input
sequence. The context position is the position of the context item
within the input sequence. For the purpose of evaluating the
context position within a predicate, the input sequence is
considered to be sorted as follows: into document order if the
predicate is in a forward-axis step, into reverse document order if
the predicate is in a reverse-axis step, or in its original order
if the predicate is not in a step.

For each item in the input sequence, the result of the predicate
expression is coerced to an xs:boolean value, called
the predicate truth value, as described below. Those items
for which the predicate truth value is true are
retained, and those for which the predicate truth value is
false are discarded.

The predicate truth value is derived by applying the following
rules, in order:

If the value of the predicate expression is a singleton atomic value of a
numeric type or derived
from a numeric type, the
predicate truth value is true if the value of the
predicate expression is equal (by the eq operator) to
the context position, and is false otherwise.
[Definition: A predicate whose predicate
expression returns a numeric type is called a numeric
predicate.]

This example selects the second chapter element
that is a child of the context node:

child::chapter[2]

This example selects all the descendants of the context node
that are elements named "toy" and whose
color attribute has the value "red":

descendant::toy[attribute::color = "red"]

This example selects all the employee children of
the context node that have both a secretary child
element and an assistant child element:

child::employee[secretary][assistant]

Note:

When using predicates with a sequence of nodes selected
using a reverse axis, it is important to remember that the
the context positions for such a sequence are assigned in reverse
document order. For example, preceding::foo[1]
returns the first qualifying foo element in reverse
document order, because the predicate is part of an axis step using a reverse
axis. By contrast, (preceding::foo)[1] returns the
first qualifying foo element in document order,
because the parentheses cause (preceding::foo) to be
parsed as a primary expression in which context
positions are assigned in document order. Similarly,
ancestor::*[1] returns the nearest ancestor element,
because the ancestor axis is a reverse axis, whereas
(ancestor::*)[1] returns the root element (first
ancestor in document order).

The fact that a reverse-axis step assigns context positions in
reverse document order for the purpose of evaluating predicates
does not alter the fact that the final result of the step
(when in ordered mode) is always in
document order.

3.2.3 Unabbreviated
Syntax

This section provides a number of examples of path expressions
in which the axis is explicitly specified in each step. The syntax used in these examples is
called the unabbreviated syntax. In many common cases, it is
possible to write path expressions more concisely using an
abbreviated syntax, as explained in 3.2.4 Abbreviated Syntax.

child::para selects the para element
children of the context node

child::* selects all element children of the
context node

child::text() selects all text node children of the
context node

child::node() selects all the children of the
context node. Note that no attribute nodes are returned, because
attributes are not children.

attribute::name selects the name
attribute of the context node

attribute::* selects all the attributes of the
context node

parent::node() selects the parent of the context
node. If the context node is an attribute node, this expression
returns the element node (if any) to which the attribute node is
attached.

descendant::para selects the para
element descendants of the context node

ancestor::div selects all div
ancestors of the context node

ancestor-or-self::div selects the div
ancestors of the context node and, if the context node is a
div element, the context node as well

descendant-or-self::para selects the
para element descendants of the context node and, if
the context node is a para element, the context node
as well

self::para selects the context node if it is a
para element, and otherwise returns an empty
sequence

child::chapter/descendant::para selects the
para element descendants of the chapter
element children of the context node

child::*/child::para selects all para
grandchildren of the context node

/ selects the root of the tree that contains the
context node, but raises a dynamic error if this root is not a
document node

/descendant::para selects all the para
elements in the same document as the context node

/descendant::list/child::member selects all the
member elements that have a list parent
and that are in the same document as the context node

child::para[fn:position() = 1] selects the first
para child of the context node

child::para[fn:position() = fn:last()] selects the
last para child of the context node

child::para[fn:position() = fn:last()-1] selects
the last but one para child of the context node

child::para[fn:position() > 1] selects all the
para children of the context node other than the first
para child of the context node

following-sibling::chapter[fn:position() = 1]
selects the next chapter sibling of the context
node

/child::book/child::chapter[fn:position() =
5]/child::section[fn:position() = 2] selects the second
section of the fifth chapter of the
book whose parent is the document node that contains
the context node

child::para[attribute::type eq "warning"] selects
all para children of the context node that have a
type attribute with value warning

child::para[attribute::type eq 'warning'][fn:position() =
5] selects the fifth para child of the context
node that has a type attribute with value
warning

child::para[fn:position() = 5][attribute::type eq
"warning"] selects the fifth para child of the
context node if that child has a type attribute with
value warning

child::chapter[child::title = 'Introduction']
selects the chapter children of the context node that
have one or more title children whose typed value is equal to
the string Introduction

child::chapter[child::title] selects the
chapter children of the context node that have one or
more title children

child::*[self::chapter or self::appendix] selects
the chapter and appendix children of the
context node

child::*[self::chapter or self::appendix][fn:position() =
fn:last()] selects the last chapter or
appendix child of the context node

3.2.4 Abbreviated Syntax

The attribute axis attribute:: can be abbreviated
by @. For example, a path expression
para[@type="warning"] is short for
child::para[attribute::type="warning"] and so selects
para children with a type attribute with
value equal to warning.

If the axis name is omitted from an axis step, the default axis is
child unless the axis step contains an AttributeTest or SchemaAttributeTest; in
that case, the default axis is attribute. For example,
the path expression section/para is an abbreviation
for child::section/child::para, and the path
expression section/@id is an abbreviation for
child::section/attribute::id. Similarly,
section/attribute(id) is an abbreviation for
child::section/attribute::attribute(id). Note that the
latter expression contains both an axis specification and a
node test.

Each non-initial occurrence of // is effectively
replaced by /descendant-or-self::node()/ during
processing of a path expression. For example,
div1//para is short for
child::div1/descendant-or-self::node()/child::para and
so will select all para descendants of
div1 children.

Note:

The path expression //para[1] does not
mean the same as the path expression
/descendant::para[1]. The latter selects the first
descendant para element; the former selects all
descendant para elements that are the first
para children of their respective parents.

A step consisting of .. is short for
parent::node(). For example, ../title is
short for parent::node()/child::title and so will
select the title children of the parent of the context
node.

Here are some examples of path expressions that use the
abbreviated syntax:

para selects the para element children
of the context node

* selects all element children of the context
node

text() selects all text node children of the
context node

@name selects the name attribute of
the context node

@* selects all the attributes of the context
node

para[1] selects the first para child
of the context node

para[fn:last()] selects the last para
child of the context node

*/para selects all para grandchildren
of the context node

/book/chapter[5]/section[2] selects the second
section of the fifth chapter of the
book whose parent is the document node that contains
the context node

chapter//para selects the para element
descendants of the chapter element children of the
context node

//para selects all the para
descendants of the root document node and thus selects all
para elements in the same document as the context
node

//@version selects all the version
attribute nodes that are in the same document as the context
node

//list/member selects all the member
elements in the same document as the context node that have a
list parent

.//para selects the para element
descendants of the context node

.. selects the parent of the context node

../@lang selects the lang attribute of
the parent of the context node

para[@type="warning"] selects all para
children of the context node that have a type
attribute with value warning

para[@type="warning"][5] selects the fifth
para child of the context node that has a
type attribute with value warning

para[5][@type="warning"] selects the fifth
para child of the context node if that child has a
type attribute with value warning

chapter[title="Introduction"] selects the
chapter children of the context node that have one or
more title children whose typed value is equal to the string
Introduction

chapter[title] selects the chapter
children of the context node that have one or more
title children

employee[@secretary and @assistant] selects all the
employee children of the context node that have both a
secretary attribute and an assistant
attribute

book/(chapter|appendix)/section selects every
section element that has a parent that is either a
chapter or an appendix element, that in
turn is a child of a book element that is a child of
the context node.

If E is any expression that returns a sequence of
nodes, then the expression E/. returns the same nodes
in document
order, with duplicates eliminated based on node identity.

3.3 Sequence Expressions

XQuery 1.1 supports operators to construct, filter, and combine
sequences of items. Sequences are never nested—for
example, combining the values 1, (2, 3),
and ( ) into a single sequence results in the sequence
(1, 2, 3).

3.3.1
Constructing Sequences

[Definition: One way to construct a sequence
is by using the comma operator, which evaluates each of its
operands and concatenates the resulting sequences, in order, into a
single result sequence.] Empty parentheses can be used to denote an
empty sequence.

A sequence may contain duplicate atomic values or nodes, but a
sequence is never an item in another sequence. When a new sequence
is created by concatenating two or more input sequences, the new
sequence contains all the items of the input sequences and its
length is the sum of the lengths of the input sequences.

Note:

In places where the grammar calls for ExprSingle, such as the arguments of
a function call, any expression that contains a top-level comma
operator must be enclosed in parentheses.

Here are some examples of expressions that construct
sequences:

The result of this expression is a sequence of five
integers:

(10, 1, 2, 3, 4)

This expression combines four sequences of length one, two,
zero, and two, respectively, into a single sequence of length five.
The result of this expression is the sequence 10, 1, 2, 3,
4.

(10, (1, 2), (), (3, 4))

The result of this expression is a sequence containing all
salary children of the context node followed by all
bonus children.

(salary, bonus)

Assuming that $price is bound to the value
10.50, the result of this expression is the sequence
10.50, 10.50.

($price, $price)

A range expression can be used to construct a sequence of
consecutive integers. Each of the operands of the to
operator is converted as though it was an argument of a function
with the expected parameter type xs:integer?. If
either operand is an empty sequence, or if the integer derived from
the first operand is greater than the integer derived from the
second operand, the result of the range expression is an empty
sequence. If the two operands convert to the same integer, the
result of the range expression is that integer. Otherwise, the
result is a sequence containing the two integer operands and every
integer between the two operands, in increasing order.

This example uses a range expression as one operand in
constructing a sequence. It evaluates to the sequence 10, 1,
2, 3, 4.

(10, 1 to 4)

This example constructs a sequence of length one containing the
single integer 10.

10 to 10

The result of this example is a sequence of length zero.

15 to 10

This example uses the fn:reverse function to
construct a sequence of six integers in decreasing order. It
evaluates to the sequence 15, 14, 13, 12, 11, 10.

fn:reverse(10 to 15)

3.3.2 Filter
Expressions

[Definition: A filter expression
consists simply of a primary expression followed by zero or
more predicates. The
result of the filter expression consists of the items returned by
the primary expression, filtered by applying each predicate in
turn, working from left to right.] If no predicates are specified,
the result is simply the result of the primary expression. The
ordering of the items returned by a filter expression is the same
as their order in the result of the primary expression. Context
positions are assigned to items based on their ordinal position in
the result sequence. The first context position is 1.

Here are some examples of filter expressions:

Given a sequence of products in a variable, return only those
products whose price is greater than 100.

If an operand of union, intersect, or
except contains an item that is not a node, a
type error is
raised [err:XPTY0004].

If an IntersectExceptExpr contains more than two
InstanceofExprs, they are grouped from left to right. With a
UnionExpr, it makes no difference how operands are grouped, the
results are the same.

Here are some examples of expressions that combine sequences.
Assume the existence of three element nodes that we will refer to
by symbolic names A, B, and C. Assume that the variables
$seq1, $seq2 and $seq3 are
bound to the following sequences of these nodes:

$seq1 is bound to (A, B)

$seq2 is bound to (A, B)

$seq3 is bound to (B, C)

Then:

$seq1 union $seq2 evaluates to the sequence (A,
B).

$seq2 union $seq3 evaluates to the sequence (A, B,
C).

$seq1 intersect $seq2 evaluates to the sequence (A,
B).

$seq2 intersect $seq3 evaluates to the sequence
containing B only.

$seq1 except $seq2 evaluates to the empty
sequence.

$seq2 except $seq3 evaluates to the sequence
containing A only.

In addition to the sequence operators described here, [XQuery and XPath Functions and Operators
1.1] includes functions for indexed access to items or
sub-sequences of a sequence, for indexed insertion or removal of
items in a sequence, and for removing duplicate items from a
sequence.

A subtraction operator must be preceded by whitespace if it
could otherwise be interpreted as part of the previous token. For
example, a-b will be interpreted as a name, but
a - b and a -b will be interpreted as
arithmetic expressions. (See A.2.4
Whitespace Rules for further details on whitespace
handling.)

If an AdditiveExpr contains more than two MultiplicativeExprs,
they are grouped from left to right. So, for instance,

A - B + C - D

is equivalent to

((A - B) + C) - D

Similarly, the operands of a MultiplicativeExpr are grouped from
left to right.

The first step in evaluating an arithmetic expression is to
evaluate its operands. The order in which the operands are
evaluated is implementation-dependent.

Each operand is evaluated by
applying the following steps, in order:

Atomization is
applied to the operand. The result of this operation is called the
atomized operand.

If the atomized operand is an empty sequence, the result of the
arithmetic expression is an empty sequence, and the implementation
need not evaluate the other operand or apply the operator. However,
an implementation may choose to evaluate the other operand in order
to determine whether it raises an error.

If the atomized operand is of type
xs:untypedAtomic, it is cast to
xs:double. If the cast fails, a dynamic error is
raised. [err:FORG0001]

After evaluation of the operands, if the types of the operands
are a valid combination for the given arithmetic operator, the
operator is applied to the operands, resulting in an atomic value
or a dynamic
error (for example, an error might result from dividing by
zero.) The combinations of atomic types that are accepted by the
various arithmetic operators, and their respective result types,
are listed in B.2 Operator Mapping
together with the operator functions that define the
semantics of the operator for each type combination, including the
dynamic errors that can be raised by the operator. The definitions
of the operator functions are found in [XQuery and XPath Functions and Operators
1.1].

XQuery 1.1 supports two division operators named
div and idiv. Each of these operators
accepts two operands of any numeric type. As described in [XQuery and XPath Functions and Operators
1.1], $arg1 idiv $arg2 is equivalent to
($arg1 div $arg2) cast as xs:integer? except for error
cases.

Here are some examples of arithmetic expressions:

The first expression below returns the xs:decimal
value -1.5, and the second expression returns the
xs:integer value -1:

-3 div 2
-3 idiv 2

Subtraction of two date values results in a value of type
xs:dayTimeDuration:

$emp/hiredate - $emp/birthdate

This example illustrates the difference between a subtraction
operator and a hyphen:

$unit-price - $unit-discount

Unary operators have higher precedence than binary operators,
subject of course to the use of parentheses. Therefore, the
following two examples have different meanings:

3.5.1 Value Comparisons

The value comparison operators are eq,
ne, lt, le, gt,
and ge. Value comparisons are used for comparing
single values.

The first step in evaluating a value comparison is to evaluate
its operands. The order in which the operands are evaluated is
implementation-dependent. Each
operand is evaluated by applying the following steps, in order:

Atomization is
applied to the operand. The result of this operation is called the
atomized operand.

If the atomized operand is an empty sequence, the result of the
value comparison is an empty sequence, and the implementation need
not evaluate the other operand or apply the operator. However, an
implementation may choose to evaluate the other operand in order to
determine whether it raises an error.

If the atomized operand is of type
xs:untypedAtomic, it is cast to
xs:string.

Note:

The purpose of this rule is to make value comparisons
transitive. Users should be aware that the general comparison
operators have a different rule for casting of
xs:untypedAtomic operands. Users should also be aware
that transitivity of value comparisons may be compromised by loss
of precision during type conversion (for example, two
xs:integer values that differ slightly may both be
considered equal to the same xs:float value because
xs:float has less precision than
xs:integer).

Next, if possible, the two operands are converted to their least
common type by a combination of type promotion and subtype
substitution. For example, if the operands are of type
hatsize (derived from xs:integer) and
shoesize (derived from xs:float), their
least common type is xs:float.

Finally, if the types of the operands are a valid combination
for the given operator, the operator is applied to the operands.
The combinations of atomic types that are accepted by the various
value comparison operators, and their respective result types, are
listed in B.2 Operator Mapping
together with the operator functions that define the
semantics of the operator for each type combination. The
definitions of the operator functions are found in [XQuery and XPath Functions and Operators
1.1].

Informally, if both atomized operands consist of exactly one
atomic value, then the result of the comparison is
true if the value of the first operand is (equal, not
equal, less than, less than or equal, greater than, greater than or
equal) to the value of the second operand; otherwise the result of
the comparison is false.

The following comparison atomizes the node(s) that are returned
by the expression $book/author. The comparison is true
only if the result of atomization is the value "Kennedy" as an
instance of xs:string or
xs:untypedAtomic. If the result of atomization is an
empty sequence, the result of the comparison is an empty sequence.
If the result of atomization is a sequence containing more than one
value, a type error
is raised [err:XPTY0004].

$book1/author eq "Kennedy"

The following path expression contains a predicate that
selects products whose weight is greater than 100. For any product
that does not have a weight subelement, the value of
the predicate is the empty sequence, and the product is not
selected. This example assumes that weight is a
validated element with a numeric type.

//product[weight gt 100]

The following comparisons are true because, in each case, the
two constructed nodes have the same value after atomization, even
though they have different identities and/or names:

<a>5</a> eq <a>5</a>

<a>5</a> eq <b>5</b>

The following comparison is true if my:hatsize and
my:shoesize are both user-defined types that are
derived by restriction from a primitive numeric type:

my:hatsize(5) eq my:shoesize(5)

The following comparison is true. The eq operator
compares two QNames by performing codepoint-comparisons of their
namespace URIs and their local names, ignoring their namespace
prefixes.

3.5.2 General Comparisons

The general comparison operators are =,
!=, <, <=,
>, and >=. General comparisons are
existentially quantified comparisons that may be applied to operand
sequences of any length. The result of a general comparison that
does not raise an error is always true or
false.

A general comparison is evaluated by
applying the following rules, in order:

Atomization is
applied to each operand. After atomization, each operand is a
sequence of atomic values.

The result of the comparison is true if and only if
there is a pair of atomic values, one in the first operand sequence
and the other in the second operand sequence, that have the
required magnitude relationship. Otherwise the result of the
comparison is false. The magnitude relationship
between two atomic values is determined by applying the following
rules. If a cast operation called for by these rules
is not successful, a dynamic error is raised. [err:FORG0001]

Note:

The purpose of these rules is to preserve compatibility with
XPath 1.0, in which (for example) x < 17 is a
numeric comparison if x is an untyped value. Users
should be aware that the value comparison operators have different
rules for casting of xs:untypedAtomic operands.

If both atomic values are instances of
xs:untypedAtomic, then the values are cast to the type
xs:string.

If exactly one of the atomic values is an instance of
xs:untypedAtomic, it is cast to a type depending on
the other value's dynamic type T according to the following rules,
in which V denotes the value to be cast:

If T is a numeric type or is derived from a numeric type, then V
is cast to xs:double.

If T is xs:dayTimeDuration or is derived from
xs:dayTimeDuration, then V is cast to
xs:dayTimeDuration.

If T is xs:yearMonthDuration or is derived from
xs:yearMonthDuration, then V is cast to
xs:yearMonthDuration.

In all other cases, V is cast to the primitive base type of
T.

Note:

The special treatment of the duration types is required to avoid
errors that may arise when comparing the primitive type
xs:duration with any duration type.

After performing the conversions described above, the atomic
values are compared using one of the value comparison operators
eq, ne, lt, le,
gt, or ge, depending on whether the
general comparison operator was =, !=,
<, <=, >, or
>=. The values have the required magnitude
relationship if and only if the result of this value comparison
is true.

When evaluating a general comparison in which either operand is
a sequence of items, an implementation may return true
as soon as it finds an item in the first operand and an item in the
second operand that have the required magnitude
relationship. Similarly, a general comparison may raise a
dynamic error
as soon as it encounters an error in evaluating either operand, or
in comparing a pair of items from the two operands. As a result of
these rules, the result of a general comparison is not
deterministic in the presence of errors.

Here are some examples of general comparisons:

The following comparison is true if the typed value of any author
subelement of $book1 is "Kennedy" as an instance of
xs:string or xs:untypedAtomic:

$book1/author = "Kennedy"

The following example contains three general comparisons. The
value of the first two comparisons is true, and the
value of the third comparison is false. This example
illustrates the fact that general comparisons are not
transitive.

(1, 2) = (2, 3)
(2, 3) = (3, 4)
(1, 2) = (3, 4)

The following example contains two general comparisons, both of
which are true. This example illustrates the fact that
the = and != operators are not inverses
of each other.

(1, 2) = (2, 3)
(1, 2) != (2, 3)

Suppose that $a, $b, and
$c are bound to element nodes with type annotation
xs:untypedAtomic, with string values "1",
"2", and "2.0" respectively. Then
($a, $b) = ($c, 3.0) returns false,
because $b and $c are compared as
strings. However, ($a, $b) = ($c, 2.0) returns
true, because $b and 2.0 are
compared as numbers.

3.5.3 Node Comparisons

Node comparisons are used to compare two nodes, by their
identity or by their document order. The result of a node
comparison is defined by the following rules:

If either operand is an empty sequence, the result of the
comparison is an empty sequence, and the implementation need not
evaluate the other operand or apply the operator. However, an
implementation may choose to evaluate the other operand in order to
determine whether it raises an error.

Each operand must be either a single node or an empty sequence;
otherwise a type
error is raised [err:XPTY0004].

A comparison with the is operator is
true if the two operand nodes have the same identity,
and are thus the same node; otherwise it is false. See
[XQuery and XPath Data Model (XDM)
1.1] for a definition of node identity.

A comparison with the << operator returns
true if the left operand node precedes the right
operand node in document order; otherwise it returns
false.

A comparison with the >> operator returns
true if the left operand node follows the right
operand node in document order; otherwise it returns
false.

Here are some examples of node comparisons:

The following comparison is true only if the left and right
sides each evaluate to exactly the same single node:

/books/book[isbn="1558604820"] is /books/book[call="QA76.9 C3845"]

The following comparison is false because each constructed node
has its own identity:

<a>5</a> is <a>5</a>

The following comparison is true only if the node identified by
the left side occurs before the node identified by the right side
in document order:

The value of an and-expression is determined by the effective
boolean values (EBV's) of its operands, as shown in the following
table:

AND:

EBV2 = true

EBV2 = false

error in EBV2

EBV1 = true

true

false

error

EBV1 = false

false

false

either false or
error

error in EBV1

error

either false or
error

error

The value of an or-expression is determined by the effective
boolean values (EBV's) of its operands, as shown in the following
table:

OR:

EBV2 = true

EBV2 = false

error in EBV2

EBV1 = true

true

true

either true or
error

EBV1 = false

true

false

error

error in EBV1

either true or
error

error

error

The order in which the operands of a
logical expression are evaluated is implementation-dependent. The
tables above are defined in such a way that an or-expression
can return true if the first expression evaluated is
true, and it can raise an error if evaluation of the first
expression raises an error. Similarly, an and-expression can return
false if the first expression evaluated is false, and
it can raise an error if evaluation of the first expression raises
an error. As a result of these rules, a logical expression is not
deterministic in the presence of errors, as illustrated in the
examples below.

Here are some examples of logical expressions:

The following expressions return true:

1 eq 1 and 2 eq 2

1 eq 1 or 2 eq 3

The following expression may return either false or
raise a dynamic
error:

1 eq 2 and 3 idiv 0 = 1

The following expression may return either true or
raise a dynamic
error:

In addition to and- and or-expressions, XQuery 1.1 provides a
function named fn:not that takes a general sequence as
parameter and returns a boolean value. The fn:not
function is defined in [XQuery and
XPath Functions and Operators 1.1]. The fn:not
function reduces its parameter to an effective boolean
value. It then returns true if the effective
boolean value of its parameter is false, and
false if the effective boolean value of its parameter
is true. If an error is encountered in finding the
effective boolean value of its operand, fn:not raises
the same error.

3.7
Constructors

XQuery provides constructors that can create XML structures
within a query. Constructors are provided for element, attribute,
document, text, comment, and processing instruction nodes. Two
kinds of constructors are provided: direct constructors,
which use an XML-like notation, and computed constructors,
which use a notation based on enclosed expressions.

This section contains a conceptual description of the semantics
of various kinds of constructor expressions. An XQuery
implementation is free to use any implementation technique that
produces the same result as the processing steps described in this
section.

3.7.1 Direct Element Constructors

An element constructor creates an element node.
[Definition: A direct element
constructor is a form of element constructor in which the name
of the constructed element is a constant.] Direct element
constructors are based on standard XML notation. For example, the
following expression is a direct element constructor that creates a
book element containing an attribute and some nested
elements:

In a direct element constructor, the name used in the end tag
must exactly match the name used in the corresponding start tag,
including its prefix or absence of a prefix.

In a direct element constructor, curly braces { } delimit
enclosed expressions, distinguishing them from literal text.
Enclosed expressions are evaluated and replaced by their value, as
illustrated by the following example:

<example>
<p> Here is a query. </p>
<eg> $b/title </eg>
<p> Here is the result of the query. </p>
<eg>{ $b/title }</eg>
</example>

The above query might generate the following result (whitespace
has been added for readability to this result and other result
examples in this document):

<example>
<p> Here is a query. </p>
<eg> $b/title </eg>
<p> Here is the result of the query. </p>
<eg><title>Harold and the Purple Crayon</title></eg>
</example>

Since XQuery uses curly braces to denote enclosed expressions,
some convention is needed to denote a curly brace used as an
ordinary character. For this purpose, a pair of identical curly
brace characters within the content of an element or attribute are
interpreted by XQuery as a single curly brace character (that is,
the pair "{{" represents the character
"{" and the pair "}}" represents the
character "}".) Alternatively, the character
references&#x7b; and &#x7d;
can be used to denote curly brace characters. A single left curly
brace ("{") is interpreted as the beginning delimiter
for an enclosed expression. A single right curly brace
("}") without a matching left curly brace is treated
as a static
error [err:XPST0003].

The result of an element constructor is a new element node, with
its own node identity. All the attribute and descendant nodes of
the new element node are also new nodes with their own identities,
even if they are copies of existing nodes.

3.7.1.1
Attributes

The start tag of a direct element constructor may contain one or
more attributes. As in XML, each attribute is specified by a name
and a value. In a direct element constructor, the name of each
attribute is specified by a constant QName, and the value of the
attribute is specified by a string of characters enclosed in single
or double quotes. As in the main content of the element
constructor, an attribute value may contain expressions enclosed in
curly braces, which are evaluated and replaced by their value
during processing of the element constructor.

If an attribute name has a namespace prefix, the prefix is
resolved to a namespace URI using the statically known namespaces. If the
attribute name has no namespace prefix, the attribute is in no
namespace. Note that the statically known namespaces used in
resolving an attribute name may be affected by namespace declaration attributes that
are found inside the same element constructor. The namespace prefix
of the attribute name is retained after expansion of the QName, as
described in [XQuery and XPath Data
Model (XDM) 1.1]. The resulting expanded QName becomes the
node-name property of the constructed attribute
node.

Conceptually, an attribute (other than a namespace declaration
attribute) in a direct element constructor is processed by the
following steps:

Each consecutive sequence of literal characters in the attribute
content is treated as a string containing those characters, with
the following exceptions:

Each occurrence of two consecutive { characters is
replaced by a single { character.

Each occurrence of two consecutive } characters is
replaced by a single } character.

Each occurrence of two consecutive " characters is
replaced by a single " character.

Each occurrence of two consecutive ' characters is
replaced by a single ' character.

Attribute value normalization is then applied to normalize
whitespace and expand character references and predefined entity references.
An XQuery processor that supports XML 1.0 uses the rules for
attribute value normalization in Section 3.3.3 of [XML 1.0]; an XQuery processor that supports XML 1.1
uses the rules for attribute value normalization in Section 3.3.3
of [XML 1.1]. In either case, the
normalization rules are applied as though the type of the attribute
were CDATA (leading and trailing whitespace characters are not
stripped.) The choice between XML 1.0 and XML 1.1 rules is
implementation-defined.

Each enclosed expression is converted to a string as
follows:

Atomization is
applied to the value of the enclosed expression, converting it to a
sequence of atomic values.

If the result of atomization is an empty sequence, the result is
the zero-length string. Otherwise, each atomic value in the
atomized sequence is cast into a string.

The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair.

Adjacent strings resulting from the above steps are concatenated
with no intervening blanks. The resulting string becomes the
string-value property of the attribute node. The
attribute node is given a type annotation (type-name
property) of xs:untypedAtomic (this type annotation
may change if the parent element is validated). The
typed-value property of the attribute node is the same
as its string-value, as an instance of
xs:untypedAtomic.

The parent property of the attribute node is set to
the element node constructed by the direct element constructor that
contains this attribute.

If the attribute name is xml:id, then
xml:id processing is performed as defined in [XML ID]. This ensures that the attribute has the type
xs:ID and that its value is properly normalized. If an
error is encountered during xml:id processing, an
implementation may raise a dynamic error [err:XQDY0091].

If the attribute name is xml:id, the
is-id property of the resulting attribute node is set
to true; otherwise the is-id property is
set to false. The is-idrefs property of
the attribute node is unconditionally set to
false.

Example:

<shoe size="7"/>

The string value of the size attribute is
"7".

Example:

<shoe size="{7}"/>

The string value of the size attribute is
"7".

Example:

<shoe size="{()}"/>

The string value of the size attribute is the
zero-length string.

Example:

<chapter ref="[{1, 5 to 7, 9}]"/>

The string value of the ref attribute is "[1
5 6 7 9]".

Example:

<shoe size="As big as {$hat/@size}"/>

The string value of the size attribute is the
string "As big as ", concatenated with the string
value of the node denoted by the expression
$hat/@size.

3.7.1.2
Namespace Declaration Attributes

The names of a constructed element and its attributes may be
QNames that include
namespace prefixes. Namespace prefixes can be bound to
namespaces in the Prolog or
by namespace declaration attributes. It is a static error to use a
namespace prefix that has not been bound to a namespace [err:XPST0081].

[Definition: A namespace declaration
attribute is used inside a direct element constructor. Its
purpose is to bind a namespace prefix or to set the default
element/type namespace for the constructed element node,
including its attributes.] Syntactically, a namespace declaration
attribute has the form of an attribute with namespace prefix
xmlns, or with name xmlns and no
namespace prefix. All the namespace declaration attributes of a
given element must have distinct names [err:XQST0071]. Each namespace declaration
attribute is processed as follows:

The value of the namespace declaration attribute (a DirAttributeValue) is
processed as follows. If the DirAttributeValue contains an
EnclosedExpr, a static
error is raised [err:XQST0022]. Otherwise, it is processed as
described in rule 1 of 3.7.1.1
Attributes. An implementation MAY raise a static error
[err:XQST0046] if
the resulting value is of nonzero length and is not in the lexical
space of xs:anyURI. The resulting value is used as the
namespace URI in the following rules.

If the prefix of the attribute name is xmlns, then
the local part of the attribute name is interpreted as a namespace
prefix. This prefix and the namespace URI are added to the
statically known namespaces of the
constructor expression (overriding any existing binding of the
given prefix), and are also added as a namespace binding to the
in-scope namespaces of the
constructed element. If the namespace URI is a zero-length string
and the implementation supports [XML Names
1.1], any existing namespace binding for the given prefix is
removed from the in-scope namespaces of the
constructed element and from the statically known namespaces of the
constructor expression. If the namespace URI is a zero-length
string and the implementation does not support [XML Names 1.1], a static error is raised
[err:XQST0085]. It
is implementation-defined whether an
implementation supports [XML Names] or
[XML Names 1.1].

If the name of the namespace declaration attribute is
xmlns with no prefix, then the namespace URI specifies
the default element/type namespace of the
constructor expression (overriding any existing default), and is
added (with no prefix) to the in-scope namespaces of the
constructed element (overriding any existing namespace binding with
no prefix). If the namespace URI is a zero-length string, the
default element/type namespace of the
constructor expression is set to "none," and any no-prefix
namespace binding is removed from the in-scope
namespaces of the constructed element.

3.7.1.3 Content

The part of a direct element constructor between the start tag
and the end tag is called the content of the element
constructor. This content may consist of text characters (parsed as
ElementContentChar),
nested direct constructors, CdataSections, character and
predefined entity references,
and expressions enclosed in curly braces. In general, the value of
an enclosed expression may be any sequence of nodes and/or atomic
values. Enclosed expressions can be used in the content of an
element constructor to compute both the content and the attributes
of the constructed node.

Conceptually, the content of an element constructor is processed
as follows:

The content is evaluated to produce a sequence of nodes called
the content sequence, as follows:

The parent property of the resulting node is then
set to the newly constructed element node.

The base-uri property of the resulting node, and of
each of its descendants, is set to be the same as that of its new
parent, unless it (the child node) has an xml:base
attribute, in which case its base-uri property is set
to the value of that attribute, resolved (if it is relative)
against the base-uri property of its new parent
node.

For each adjacent sequence of one or more atomic values returned
by an enclosed expression, a new text node is constructed,
containing the result of casting each atomic value to a string,
with a single space character inserted between adjacent values.

Note:

The insertion of blank characters between adjacent values
applies even if one or both of the values is a zero-length
string.

For each node returned by an enclosed expression, a new copy is
made of the given node and all nodes that have the given node as an
ancestor, collectively referred to as copied nodes. The
properties of the copied nodes are as follows:

Each copied node receives a new node identity.

The parent, children, and
attributes properties of the copied nodes are set so
as to preserve their inter-node relationships. For the topmost node
(the node directly returned by the enclosed expression), the
parent property is set to the node constructed by this
constructor.

If the copied node is an element node, its
type-name property is set to xs:untyped.
Its nilled, is-id, and
is-idrefs properties are set to
false.

If the copied node is an attribute node, its
type-name property is set to
xs:untypedAtomic. Its is-idrefs property
is set to false. Its is-id property is
set to true if the qualified name of the attribute
node is xml:id; otherwise it is set to
false.

The string-value of each copied element and
attribute node remains unchanged, and its typed-value
becomes equal to its string-value as an instance of
xs:untypedAtomic.

Note:

Implementations that store only the typed value of a node are required at this
point to convert the typed value to a string form.

On the other hand, if construction mode in the static context is
preserve, the type-name,
nilled, string-value,
typed-value, is-id, and
is-idrefs properties of the copied nodes are
preserved.

The in-scope-namespaces property of a copied
element node is determined by the following rules. In applying
these rules, the default namespace or absence of a default
namespace is treated like any other namespace binding:

If copy-namespaces mode specifies
preserve, all in-scope-namespaces of the original
element are retained in the new copy. If copy-namespaces mode specifies
no-preserve, the new copy retains only those in-scope
namespaces of the original element that are used in the names of
the element and its attributes.

If copy-namespaces mode specifies
inherit, the copied node inherits all the in-scope
namespaces of the constructed node, augmented and overridden by the
in-scope namespaces of the original element that were preserved by
the preceding rule. If copy-namespaces mode specifies
no-inherit, the copied node does not inherit any
in-scope namespaces from the constructed node.

An enclosed expression in the content of an element constructor
may cause one or more existing nodes to be copied. Type error
[err:XQTY0086] is
raised in the following cases:

[Definition: A value is
namespace-sensitive if it includes an item whose dynamic type is
xs:QName or xs:NOTATION or is derived by
restriction from xs:QName or
xs:NOTATION.]

Note:

The rationale for error [err:XQTY0086] is as follows: It is not possible
to preserve the type of a QName without also preserving the
namespace binding that defines the prefix of the QName.

When an element or processing instruction node is copied, its
base-uri property is set to be the same as that of its
new parent, with the following exception: if a copied element node
has an xml:base attribute, its base-uri
property is set to the value of that attribute, resolved (if it is
relative) against the base-uri property of the new
parent node.

All other properties of the copied nodes are preserved.

If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.

Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.

If the content sequence contains an attribute node or a
namespace node following a node that is not an attribute node or a
namespace node, a type
error is raised [err:XQTY0024].

The properties of the newly constructed element node are
determined as follows:

attributes consist of all the attributes specified
in the start tag as described in 3.7.1.1 Attributes, together with all
the attribute nodes in the content sequence, in implementation-dependent order.
Note that the parent property of each of these
attribute nodes has been set to the newly constructed element node.
If two or more attributes have the same node-name, a
dynamic error
is raised [err:XQDY0025]. If an attribute named
xml:space has a value other than preserve
or default, a dynamic error may be raised [err:XQDY0092].

children consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the parent property of each of these nodes has been
set to the newly constructed element node.

base-uri is set to the following value:

If the constructed node has an attribute named
xml:base, then the value of this attribute, resolved
if it is relative against the base URI in the static context. The value of the
xml:base attribute is normalized as described in
[XML Base].

The string-value property is equal to the
concatenated contents of the text-node descendants in document
order. If there are no text-node descendants, the
string-value property is a zero-length string.

The typed-value property is equal to the
string-value property, as an instance of
xs:untypedAtomic.

If construction mode in the static context is
strip, the type-name property is
xs:untyped. On the other hand, if construction mode is
preserve, the type-name property is
xs:anyType.

The is-id and is-idrefs properties are
set to false.

Example:

<a>{1}</a>

The constructed element node has one child, a text node
containing the value "1".

Example:

<a>{1, 2, 3}</a>

The constructed element node has one child, a text node
containing the value "1 2 3".

Example:

<c>{1}{2}{3}</c>

The constructed element node has one child, a text node
containing the value "123".

Example:

<b>{1, "2", "3"}</b>

The constructed element node has one child, a text node
containing the value "1 2 3".

The constructed element node has three children: a text node
containing "I saw ", a child element node named
howmany, and a text node containing "
cats.". The child element node in turn has a single
text node child containing the value "8".

3.7.1.4 Boundary
Whitespace

In a direct element constructor, whitespace characters may
appear in the content of the constructed element. In some cases,
enclosed expressions and/or nested elements may be separated only
by whitespace characters. For example, in the expression below, the
end-tag </title> and the start-tag
<author> are separated by a newline character
and four space characters:

The boundary-space policy in the
static
context controls whether boundary whitespace is preserved by
element constructors. If boundary-space policy is
strip, boundary whitespace is not considered
significant and is discarded. On the other hand, if boundary-space
policy is preserve, boundary whitespace is considered
significant and is preserved.

Example:

<cat>
<breed>{$b}</breed>
<color>{$c}</color>
</cat>

The constructed cat element node has two child
element nodes named breed and color.
Whitespace surrounding the child elements will be stripped away by
the element constructor if boundary-space policy is
strip.

Example:

<a> {"abc"} </a>

If boundary-space policy is strip, this example is
equivalent to <a>abc</a>. However, if
boundary-space policy is preserve, this example is
equivalent to
<a> abc </a>.

Example:

<a> z {"abc"}</a>

Since the whitespace surrounding the z is not
boundary whitespace, it is always preserved. This example is
equivalent to <a> z abc</a>.

Example:

<a>&#x20;{"abc"}</a>

This example is equivalent to
<a> abc</a>, regardless of the
boundary-space policy, because the space generated by the character
reference is not treated as a whitespace character.

Example:

<a>{" "}</a>

This example constructs an element containing two space
characters, regardless of the boundary-space policy, because
whitespace inside an enclosed expression is never considered to be
boundary whitespace.

Note:

Element constructors treat attributes named
xml:space as ordinary attributes. An
xml:space attribute does not affect the handling of
whitespace by an element constructor.

3.7.2 Other Direct Constructors

XQuery allows an expression to generate a processing instruction
node or a comment node. This can be accomplished by using a
direct processing instruction constructor or a direct
comment constructor. In each case, the syntax of the
constructor expression is based on the syntax of a similar
construct in XML.

A direct processing instruction constructor creates a processing
instruction node whose target property is PITarget and whose
content property is DirPIContents. The
base-uri property of the node is empty. The
parent property of the node is empty.

The PITarget of a
processing instruction must not consist of the characters "XML" in
any combination of upper and lower case. The DirPIContents of a processing
instruction must not contain the string "?>".

The following example illustrates a direct processing
instruction constructor:

The DirCommentContents of a
comment must not contain two consecutive hyphens or end with a
hyphen. These rules are syntactically enforced by the grammar shown
above.

The following example illustrates a direct comment
constructor:

<!-- Tags are ignored in the following section -->

Note:

A direct comment constructor is different from a comment, since a direct comment
constructor actually constructs a comment node, whereas a comment is simply used in documenting a
query and is not evaluated.

3.7.3 Computed Constructors

An alternative way to create nodes is by using a computed
constructor. A computed constructor begins with a keyword that
identifies the type of node to be created: element,
attribute, document, text,
processing-instruction, comment, or
namespace.

For those kinds of nodes that have names (element, attribute,
and processing instruction nodes), the keyword that specifies the
node kind is followed by the name of the node to be created. This
name may be specified either as a QName or as an expression
enclosed in braces. [Definition: When
an expression is used to specify the name of a constructed node,
that expression is called the name expression of the
constructor.]

[Definition: The final part of a
computed constructor is an expression enclosed in braces, called
the content expression of the constructor, that generates
the content of the node.]

The following example illustrates the use of computed element
and attribute constructors in a simple case where the names of the
constructed nodes are constants. This example generates exactly the
same result as the first example in 3.7.1 Direct Element
Constructors:

A static
error is raised [ERROR 0044 NOT FOUND] if the node-name of the
constructed element node has any of the following properties:

Its namespace prefix is xmlns.

It has no namespace prefix and its local name is
xmlns.

Its namespace URI is
http://www.w3.org/2000/xmlns/.

Its namespace prefix is xml and its namespace URI
is not http://www.w3.org/XML/1998/namespace.

Its namespace prefix is other than xml and its
namespace URI is
http://www.w3.org/XML/1998/namespace.

The content expression of a computed
element constructor (if present) is processed in exactly the same
way as an enclosed expression in the content of a direct
element constructor, as described in Step 1e of 3.7.1.3 Content. The result of processing
the content expression is a sequence of nodes called the content
sequence. If the content expression is absent, the
content sequence is an empty sequence.

Processing of the computed element constructor proceeds as
follows:

If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.

Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.

If the content sequence contains an attribute node or a
namespace node following a node that is not an attribute node or a
namespace node, a type
error is raised [err:XQTY0024].

The properties of the newly constructed element node are
determined as follows:

attributes consist of all the attribute nodes in
the content sequence, in implementation-dependent order.
Note that the parent property of each of these
attribute nodes has been set to the newly constructed element node.
If two or more attributes have the same node-name, a
dynamic error
is raised [err:XQDY0025]. If an attribute named
xml:space has a value other than preserve
or default, a dynamic error may be raised [err:XQDY0092].

children consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the parent property of each of these nodes has been
set to the newly constructed element node.

base-uri is set to the following value:

If the constructed node has an attribute named
xml:base, then the value of this attribute, resolved
if it is relative against the base URI in the static context. The value of the
xml:base attribute is normalized as described in
[XML Base].

The string-value property is equal to the
concatenated contents of the text-node descendants in document
order.

The typed-value property is equal to the
string-value property, as an instance of
xs:untypedAtomic.

If construction mode in the static context is
strip, the type-name property is
xs:untyped. On the other hand, if construction mode is
preserve, the type-name property is
xs:anyType.

The is-id and is-idrefs properties are
set to false.

A computed element constructor might be used to make a modified
copy of an existing element. For example, if the variable
$e is bound to an element with numeric content, the following constructor
might be used to create a new element with the same name and
attributes as $e and with numeric content equal to
twice the value of $e:

element {fn:node-name($e)}
{$e/@*, 2 * fn:data($e)}

In this example, if $e is bound by the expression
let $e := <length
units="inches">{5}</length>, then the result of the
example expression is the element <length
units="inches">10</length>.

Note:

The static
type of the expression fn:node-name($e) is
xs:QName?, denoting zero or one QName. Therefore, if
the Static Typing Feature is in effect,
the above example raises a static type error, since the name
expression in a computed element constructor is required to return
exactly one string or QName. In order to avoid the static type
error, the name expression fn:node-name($e) could be
rewritten as fn:exactly-one(fn:node-name($e)). If the
Static Typing Feature is not in
effect, the example can be successfully evaluated as written,
provided that $e is bound to exactly one element node
with numeric content.

One important purpose of computed constructors is to allow the
name of a node to be computed. We will illustrate this feature by
an expression that translates the name of an element from one
language to another. Suppose that the variable $dict
is bound to a dictionary element containing a sequence
of entry elements, each of which encodes translations
for a specific word. Here is an example entry that encodes the
German and Italian variants of the word "address":

Suppose further that the variable $e is bound to
the following element:

<address>123 Roosevelt Ave. Flushing, NY 11368</address>

Then the following expression generates a new element in which
the name of $e has been translated into Italian and
the content of $e (including its attributes, if any)
has been preserved. The first enclosed expression after the
element keyword generates the name of the element, and
the second enclosed expression generates the content and
attributes:

As in the previous example, if the Static
Typing Feature is in effect, the enclosed expression that
computes the element name in the above computed element constructor
must be wrapped in a call to the fn:exactly-one
function in order to avoid a static type error.

If the result of atomization is an empty sequence, the value of
the attribute is the zero-length string. Otherwise, each atomic
value in the atomized sequence is cast into a string.

The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
string-value property of the new attribute node. The
type
annotation (type-name property) of the new
attribute node is xs:untypedAtomic. The
typed-value property of the attribute node is the same
as its string-value, as an instance of
xs:untypedAtomic.

The parent property of the attribute node is set to
empty.

If the attribute name is xml:id, then
xml:id processing is performed as defined in [XML ID]. This ensures that the attribute node has the
type xs:ID and that its value is properly normalized.
If an error is encountered during xml:id processing,
an implementation may raise a dynamic error [err:XQDY0091].

If the attribute name is xml:id, the
is-id property of the resulting attribute node is set
to true; otherwise the is-id property is
set to false. The is-idrefs property of
the attribute node is unconditionally set to
false.

If the attribute name is xml:space and the
attribute value is other than preserve or
default, a dynamic error MAY be raised [err:XQDY0092].

Example:

attribute size {4 + 3}

The string
value of the size attribute is "7"
and its type is xs:untypedAtomic.

3.7.3.3 Document Node
Constructors

All document node constructors are computed constructors. The
result of a document node constructor is a new document node, with
its own node identity.

A document node constructor is useful when the result of a query
is to be a document in its own right. The following example
illustrates a query that returns an XML document containing a root
element named author-list:

The content expression of a document node
constructor is processed in exactly the same way as an enclosed
expression in the content of a direct
element constructor, as described in Step 1e of 3.7.1.3 Content. The result of processing
the content expression is a sequence of nodes called the content
sequence. Processing of the document node constructor then
proceeds as follows:

If the content sequence contains a document node, the document
node is replaced in the content sequence by its children.

Adjacent text nodes in the content sequence are merged into a
single text node by concatenating their contents, with no
intervening blanks. After concatenation, any text node whose
content is a zero-length string is deleted from the content
sequence.

The properties of the newly constructed document node are
determined as follows:

base-uri is taken from base URI in the static context. If no base URI is defined in the
static context, the base-uri property is empty.

children consist of all the element, text, comment,
and processing instruction nodes in the content sequence. Note that
the parent property of each of these nodes has been
set to the newly constructed document node.

The unparsed-entities and document-uri
properties are empty.

The string-value property is equal to the
concatenated contents of the text-node descendants in document
order.

The typed-value property is equal to the
string-value property, as an instance of
xs:untypedAtomic.

No validation is performed on the constructed document node. The
[XML 1.0] rules that govern the structure of an
XML document (for example, the document node must have exactly one
child that is an element node) are not enforced by the XQuery
document node constructor.

If the result of atomization is an empty sequence, no text node
is constructed. Otherwise, each atomic value in the atomized
sequence is cast into a string.

The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
content property of the constructed text node.

The parent property of the constructed text node is
set to empty.

Note:

It is possible for a text node constructor to construct a text
node containing a zero-length string. However, if used in the
content of a constructed element or document node, such a text node
will be deleted or merged with another text node.

3.7.3.5
Computed Processing Instruction Constructors

A computed processing instruction constructor (CompPIConstructor) constructs
a new processing instruction node with its own node identity.

If the keyword processing-instruction is followed
by an NCName, that NCName is used as the target
property of the constructed node. If the keyword
processing-instruction is followed by a name expression,
the name expression is processed as follows:

If the atomized value of the name expression is of type
xs:string or xs:untypedAtomic, that value
is cast to the type xs:NCName. If the value cannot be
cast to xs:NCName, a dynamic error is raised [err:XQDY0041].

The resulting NCName is then used as the target
property of the newly constructed processing instruction node.
However, a dynamic error is raised if the NCName is
equal to "XML" (in any combination of upper and lower
case) [err:XQDY0064].

The content expression of a computed
processing instruction constructor is processed as follows:

If the result of atomization is an empty sequence, it is
replaced by a zero-length string. Otherwise, each atomic value in
the atomized sequence is cast into a string. If any of the
resulting strings contains the string "?>", a
dynamic error
[err:XQDY0026] is
raised.

The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. Leading whitespace is removed
from the resulting string. The resulting string then becomes the
content property of the constructed processing
instruction node.

The remaining properties of the new processing instruction node
are determined as follows:

The parent property is empty.

The base-uri property is empty.

The following example illustrates a computed processing
instruction constructor:

If the result of atomization is an empty sequence, it is
replaced by a zero-length string. Otherwise, each atomic value in
the atomized sequence is cast into a string.

The individual strings resulting from the previous step are
merged into a single string by concatenating them with a single
space character between each pair. The resulting string becomes the
content property of the constructed comment node.

If the result of atomization is a single atomic value of type
xs:NCName, xs:string, or
xs:untypedAtomic, it is used as the
prefix property of the newly constructed namespace
node. If the result is the empty sequence or an empty string, the
prefix property of the newly constructed namespace
node is empty. For any other result, a type error is raised [err:XPTY0004].

The URIExpr is evaluated, and the result is cast to
xs:anyURI to create the URI property for
the newly created node.

An error [err:XQDY0101] is raised if the namespace URI in
a computed namespace constructor is bound to the predefined prefix
xmlns, or if a namespace URI other than
http://www.w3.org/XML/1998/namespace is bound to the
prefix xml, or if the prefix xml is bound
to a namespace URI other than
http://www.w3.org/XML/1998/namespace.

By itself, a computed namespace constructor has no effect on
in-scope namespaces, but if an element constructor's content
sequence contains a namespace node, the namespace binding it
represents is added to the elements in-scope namespaces.

A computed namespace constructor has no effect on the statically
known namespaces.

Note:

The newly created namespace node has all properties defined for
a namespace node in the data model. Like all nodes, it has
identity. Like all nodes which do not share a common parent, the
relative order of these nodes is implementation dependent. As
defined in the data model, the name of the node is the prefix, and
the string value of the node is the URI.

Examples:

A computed namespace constructor with a prefix:

namespace a {"http://a.example.com" }

A computed namespace constructor with a prefix expression:

namespace {"a"} {"http://a.example.com" }

A computed namespace constructor with an empty prefix:

namespace { "" } {"http://a.example.com" }

Computed namespace constructors are generally used to add to the
in-scope namespaces of elements created with element
constructors:

Computed namespace constructors have no effect on the statically
known namespaces. If the prefix a is not already defined in the
statically known namespaces, the following expression results in a
static error [err:XPST0081].

<a:form>
{
namespace a { "http://a.example.com" }
}
</a:form>

3.7.4 In-scope Namespaces of a
Constructed Element

An element node constructed by a direct or computed element
constructor has an in-scope namespaces property that
consists of a set of namespace bindings. The in-scope
namespaces of an element node may affect the way the node is
serialized (see 2.2.4
Serialization), and may also affect the behavior of certain
functions that operate on nodes, such as fn:name. Note
the difference between in-scope namespaces, which is a
dynamic property of an element node, and statically known namespaces, which is a
static property of an expression. Also note that one of the
namespace bindings in the in-scope namespaces may have no prefix
(denoting the default namespace for the given element). The
in-scope namespaces of a constructed element node consist of the
following namespace bindings:

A namespace binding is always created to bind the prefix
xml to the namespace URI
http://www.w3.org/XML/1998/namespace.

For each namespace used in the name of the constructed element
or in the names of its attributes, a namespace binding must exist.
If a namespace binding does not already exist for one of these
namespaces, a new namespace binding is created for it. If the name
of the node includes a prefix, that prefix is used in the namespace
binding; if the name has no prefix, then a binding is created for
the empty prefix. If this would result in a conflict, because it
would require two different bindings of the same prefix, then the
prefix used in the node name is changed to an arbitrary implementation-dependent prefix
that does not cause such a conflict, and a namespace binding is
created for this new prefix.

Note:

Copy-namespaces mode does not affect
the namespace bindings of a newly constructed element node. It
applies only to existing nodes that are copied by a constructor
expression.

In an element constructor, if two or more namespace bindings in
the in-scope bindings would have the same prefix, then an error is
raised if they have different URIs [err:XQTY0102]; if they would have the same
prefix and URI, duplicate bindings are ignored.

The namespace bindings for p and q are
added to the result element because their respective namespaces are
used in the names of the element and its attributes. The namespace
binding r="http://example.com/ns/r" is added to the
in-scope namespaces of the constructed element because it is
defined by a namespace declaration attribute, even
though it is not used in a name.

No namespace binding corresponding to
f="http://example.com/ns/f" is created, because the
namespace prefix f appears only in the query prolog
and is not used in an element or attribute name of the constructed
node. This namespace binding does not appear in the query result,
even though it is present in the statically known namespaces and is
available for use during processing of the query.

Note that the following constructed element, if nested within a
validate expression, cannot be validated:

<p xsi:type="xs:integer">3</p>

The constructed element will have namespace bindings for the
prefixes xsi (because it is used in a name) and
xml (because it is defined for every constructed
element node). During validation of the constructed element, the
validator will be unable to interpret the namespace prefix
xs because it is has no namespace binding. Validation
of this constructed element could be made possible by providing a
namespace declaration attribute, as
in the following example:

3.8 FLWOR Expressions

XQuery provides a versatile expression called a FLWOR expression
that may contain multiple clauses. The FLWOR expression can be used
for many purposes, including iterating over sequences, joining
multiple documents, and performing grouping and aggregation. The
name FLWOR, pronounced "flower", is suggested by the keywords
for, let, where, order
by, and return, which introduce some of the
clauses used in FLWOR expressions (but this is not a complete list
of such clauses.)

The complete syntax of a FLWOR expression is shown here, and
relevant parts of the syntax are repeated in subsequent sections of
this document.

The semantics of FLWOR expressions are based on a concept called
a tuple stream. [Definition: A tuple stream is
an ordered sequence of zero or more tuples.] [Definition:
A tuple is a set of zero or more named variables, each of
which is bound to a value that is an XDM instance.] Each tuple stream is
homogeneous in the sense that all its tuples contain variables with
the same names and the same static types. The following example
illustrates a tuple stream consisting of four tuples, each
containing three variables named $x, $y,
and $z:

In this section, tuple streams are represented as shown in the
above example. Each tuple is on a separate line and is enclosed in
parentheses, and the variable bindings inside each tuple are
separated by commas. This notation does not represent XQuery
syntax, but is simply a representation of a tuple stream for the
purpose of defining the semantics of FLWOR expressions.

Tuples and tuple streams are not part of the data model. They exist only
as conceptual intermediate results during the processing of a FLWOR
expression.

A FLWOR expression consists of an initial clause, zero or more
intermediate clauses, and a final clause. Conceptually, the initial
clause generates a tuple stream. Each intermediate clause takes the
tuple stream generated by the previous clause as input and
generates a (possibly different) tuple stream as output. The final
clause takes a tuple stream as input and, for each tuple in this
tuple stream, generates an XDM instance; the final result of the
FLWOR expression is the ordered concatenation of these XDM
instances.

The initial clause in a FLWOR expression may be a
for, let, window, or
count clause. Intermediate clauses may be
for, let, window,
count, where, group by, or
order by clauses. These intermediate clauses may be
repeated as many times as desired, in any order. The final clause
of the FLWOR expression must be a return clause. The
semantics of the various clauses are described in the following
sections.

3.8.1
Variable Bindings

The following clauses in FLWOR expressions bind values to
variables: for, let, window,
and count (in addition, a group by clause
changes the values of variables that were previously bound.) In
each case, binding of variables is governed by the following
rules:

The scope of a bound variable includes all subexpressions of the
containing FLWOR that appear after the variable binding. The scope
does not include the expression to which the variable is bound. The
following code fragment, containing two let clauses,
illustrates how variable bindings may reference variables that were
bound in earlier clauses, or in earlier bindings in the same
clause:

let $x := 47, $y := f($x)
let $z := g($x, $y)

A given variable may be bound more than once in a FLWOR
expression, or even within one clause of a FLWOR expression. In
such a case, each new binding occludes the previous one, which
becomes inaccessible in the remainder of the FLWOR expression.

[Definition: A variable binding may be
accompanied by a type declaration, which consists of the
keyword as followed by the static type of the
variable, declared using the syntax in 2.5.3 SequenceType Syntax.] At
run time, if the value bound to the variable does not match the
declared type according to the rules for SequenceType matching, a type error is raised
[err:XPTY0004]. For
example, the following let clause raises a type error because the
variable $salary has a type declaration that is not
satisfied by the value that is bound to it:

let $salary as xs:decimal := "cat"

[Definition: In a for clause
or window clause, when an expression is preceded by
the keyword in, the value of that expression is called
a binding sequence.] The for and
window clauses iterate over their binding sequences,
producing multiple bindings for one or more variables. Details on
how binding sequences are used in for and
window clauses are described in the following
sections.

A for clause is used for iteration. Each variable
in a for clause iterates over a sequence and is bound
in turn to each item in the sequence.

If a for clause contains multiple variables, it is
semantically equivalent to multiple for clauses, each
containing one of the variables in the original for
clause.

Example:

The clause

for $x in $expr1, $y in $expr2

is semantically equivalent to:

for $x in $expr1
for $y in $expr2

In the remainder of this section, we define the semantics of a
for clause containing a single variable and an
associated expression (following the keyword in) whose
value is called the binding sequence for that variable.

If a single-variable for clause is the initial
clause in a FLWOR expression, it iterates over its binding
sequence, binding the variable to each item in turn. The
resulting sequence of variable bindings becomes the initial tuple
stream that serves as input to the next clause of the FLWOR
expression. If ordering mode is ordered, the
order of tuples in the tuple stream preserves the order of the
binding
sequence; otherwise the order of the tuple stream is implementation-dependent.

If the binding sequence contains no items, the
output tuple stream depends on whether allowing empty
is specified. If allowing empty is specified, the
output tuple stream consists of one tuple in which the variable is
bound to an empty sequence. If allowing empty is not
specified, the output tuple stream consists of zero tuples.

The following examples illustrates tuple streams that are
generated by initial for clauses:

Initial clause:

for $x in (100, 200, 300)

or (equivalently):

for $x allowing empty in (100, 200, 300)

Output tuple stream:

($x = 100)
($x = 200)
($x = 300)

Initial clause:

for $x in ()

Output tuple stream contains no tuples.

Initial clause:

for $x allowing empty in ()

Output tuple stream:

($x = ())

[Definition: A positional
variable is a variable that is preceded by the keyword
at.] A positional variable may be associated with a
variable that is bound in a for clause. In this case,
as the main variable iterates over the items in its binding
sequence, the positional variable iterates over the integers
that represent the ordinal numbers of these items in the binding
sequence, starting with one. Each tuple in the output tuple
stream contains bindings for both the main variable and the
positional variable. If the binding sequence is empty and
allowing empty is specified, the positional variable
in the output tuple is bound to the integer zero. Positional
variables always have the implied type xs:integer. The
expanded
QName of a positional variable must be distinct from the
expanded
QName of the main variable with which it is associated
[err:XQST0089].

The following examples illustrate how a positional variable
would have affected the results of the previous examples that
generated tuples:

Initial clause:

for $x at $i in (100, 200, 300)

Output tuple stream:

($x = 100, $i = 1)
($x = 200, $i = 2)
($x = 300, $i = 3)

Initial clause:

for $x allowing empty at $i in ()

Output tuple stream:

($x = (), $i = 0)

If a single-variable for clause is an intermediate
clause in a FLWOR expression, its binding sequence is evaluated for each
input tuple, given the bindings in that input tuple. Each input
tuple generates zero or more tuples in the output tuple stream.
Each of these output tuples consists of the original variable
bindings of the input tuple plus a binding of the new variable to
one of the items in its binding sequence.

Note:

Although the binding sequence is conceptually
evaluated independently for each input tuple, an optimized
implementation may sometimes be able to avoid re-evaluating the
binding
sequence if it can show that the variables that the binding sequence
depends on have the same values as in a previous evaluation.

For a given input tuple, if the binding sequence for the new
variable in the for clause contains no items, the
result depends on whether allowing empty is specified.
If allowing empty is specified, the input tuple
generates one output tuple, with the original variable bindings
plus a binding of the new variable to an empty sequence. If
allowing empty is not specified, the input tuple
generates zero output tuples (it is not represented in the output
tuple stream.)

If ordering
mode is ordered, the tuples in the output tuple
stream are ordered primarily by the order of the input tuples from
which they are derived, and secondarily by the order of the
binding
sequence for the new variable; otherwise the order of the
output tuple stream is implementation-dependent.

The following examples illustrates the effects of intermediate
for clauses:

In this example, there is no output tuple that corresponds to
the input tuple ($x = 4) because, when the
for clause is evaluated with the bindings in this
input tuple, the resulting binding sequence for $y is
empty.

This example shows how the previous example would have been
affected by a positional variable (assuming the
same input tuple stream):

This example shows how the previous example would have been
affected by allowing empty. Note that allowing
empty causes the input tuple ($x = 4) to be
represented in the output tuple stream, even though the binding sequence
for $y contains no items for this input tuple. This
example illustrates that allowing empty in a
for clause serves a purpose similar to that of an
"outer join" in a relational database query. (Assume the same input
tuple stream as in the previous example.)

This example shows how a for clause that binds two
variables is semantically equivalent to two for
clauses that bind one variable each. We assume that this
for clause occurs at the beginning of a FLWOR
expression. It is equivalent to an initial single-variable
for clause that provides an input tuple stream to an
intermediate single-variable for clause.

3.8.3 Let Clause

The purpose of a let clause is to bind values to
one or more variables. Each variable is bound to the result of
evaluating an expression.

If a let clause contains multiple variables, it is
semantically equivalent to multiple let clauses, each
containing a single variable. For example, the clause

let $x := $expr1, $y := $expr2

is semantically equivalent to the following sequence of
clauses:

let $x := $expr1
let $y := $expr2

In the remainder of this section, we define the semantics of a
let clause containing a single variable V and
an associated expression E.

If a single-variable let clause is the initial
clause in a FLWOR expression, it simply binds the variable
V to the result of the expression E. The result
of the let clause is a tuple stream consisting of one
tuple with a single binding that binds V to the result of
E. This tuple stream serves as input to the next clause in
the FLWOR expression.

If a single-variable let clause is an intermediate
clause in a FLWOR expression, it adds a new binding for variable
V to each tuple in the input tuple stream. For each input
tuple, the value bound to V is the result of evaluating
expression E, given the bindings that are already present
in that input tuple. The resulting tuples become the output tuple
stream of the let clause.

The number of tuples in the output tuple stream of an
intermediate let clause is the same as the number of
tuples in the input tuple stream. The number of bindings in the
output tuples is one more than the number of bindings in the input
tuples, unless the input tuples already contain bindings for
V; in this case, the new binding for V occludes
(replaces) the earlier binding for V, and the number of
bindings is unchanged.

The following code fragment illustrates how a for
clause and a let clause can be used together. The
for clause produces an initial tuple stream containing
a binding for variable $d to each department number
found in a given input document. The let clause adds
an additional binding to each tuple, binding variable
$e to a sequence of employees whose department number
matches the value of $d in that tuple.

Like a for clause, a window clause
iterates over its binding sequence and generates a
sequence of tuples. In the case of a window clause,
each tuple represents a window. [Definition: A window is a sequence of
consecutive items drawn from the binding sequence.] Each window is
represented by at least one and at most nine bound variables. The
variables have user-specified names, but their roles are as
follows:

Window-variable: Bound to the sequence of items from
the binding
sequence that comprise the window.

Start-item: (Optional) Bound to the first item in the
window.

Start-item-position: (Optional) Bound to the ordinal
position of the first window item in the binding
sequence. Start-item-position is a positional
variable. Its type is xs:integer, and its expanded
QName must be distinct from the expanded QName of
start-item [err:XQST0089].

Start-previous-item: (Optional) Bound to the item in
the binding
sequence that precedes the first item in the window (empty
sequence if none).

Start-next-item: (Optional) Bound to the item in the
binding
sequence that follows the first item in the window (empty
sequence if none).

End-item: (Optional) Bound to the last item in the
window.

End-item-position: (Optional) Bound to the ordinal
position of the last window item in the binding sequence.
End-item-position is a positional variable. Its type is
xs:integer, and its expanded QName must be distinct
from the expanded QName of end-item [err:XQST0089].

End-previous-item: (Optional) Bound to the item in the
binding
sequence that precedes the last item in the window (empty
sequence if none).

End-next-item: (Optional) Bound to the item in the
binding
sequence that follows the last item in the window (empty
sequence if none).

The following is an example of a window clause that
binds nine variables to the roles listed above. In this example,
the variables are named $w, $s,
$spos, $sprev, $snext,
$e, $epos, $eprev, and
$enext respectively. A window clause
always binds the window variable, but typically binds only a subset
of the other variables.

for tumbling window $w in (2, 4, 6, 8, 10)
start $s at $spos previous $sprev next $snext when true() end $e at
$epos previous $eprev next $enext when true()

The scoping rules for the variables bound by a
window clause are as follows:

In the when-expression of the WindowStartCondition, the
following variables (identified here by their roles) are in scope
(if bound): start-item, start-item-position,
start-previous-item, start-next-item.

In the when-expression of the WindowEndCondition, the
following variables (identified here by their roles) are in scope
(if bound): start-item, start-item-position,
start-previous-item, start-next-item, end-item, end-item-position,
end-previous-item, end-next-item.

In the clauses of the FLWOR expression that follow the
window clause, all nine of the variables bound by the
window clause (including window-variable) are
in scope (if bound).

In a window clause, the keyword
tumbling or sliding determines the way in
which the starting item of each window is identified, as explained
in the following sections.

3.8.4.1 Tumbling Windows

If the window type is tumbling, then windows never
overlap. The search for the start of the first window begins at the
beginning of the binding sequence. After each window is
generated, the search for the start of the next window begins with
the item in the binding sequence that occurs after the
ending item of the last generated window. Thus, no item that occurs
in one window can occur in another window drawn from the same
binding
sequence. In a tumbling window clause, the end
clause is optional; if it is omitted, the start clause
is applied to identify all potential starting items in the
binding
sequence, and a window is constructed for each starting item,
including all items from that starting item up to the item before
the next window's starting item, or the end of the binding
sequence, whichever comes first.

3.8.4.2 Sliding Windows

If the window type is sliding window, then windows
may overlap. Every item in the binding sequence that satisfies the
WindowStartCondition is
the starting item of a new window. Thus, a given item may be found
in multiple windows drawn from the same binding sequence.

3.8.4.3 Effects of Window
Clauses on the Tuple Stream

The effects of a window clause on the tuple stream
are similar to the effects of a for clause. As
described in 3.8.4 Window Clause,
a window clause generates zero or more windows, each
of which is represented by at least one and at most nine bound
variables.

If the window clause is the initial clause in a
FLWOR expression, the bound variables that describe each window
become an output tuple. These tuples form the initial tuple stream
that serves as input to the next clause of the FLWOR expression. If
ordering mode
is ordered, the order of tuples in the tuple stream is
the order in which their start items appear in the binding
sequence; otherwise the order of the tuple stream is implementation-dependent. The
cardinality of the tuple stream is equal to the number of
windows.

If a window clause is an intermediate clause in a
FLWOR expression, each input tuple generates zero or more output
tuples, each consisting of the original bound variables of the
input tuple plus the new bound variables that represent one of the
generated windows. For each tuple T in the input tuple
stream, the output tuple stream will contain NT
tuples, where NT is the number of windows
generated by the window clause, given the bindings in
the input tuple T. Input tuples for which no windows are
generated are not represented in the output tuple stream. If
ordering mode
is ordered, the order of tuples in the output stream
is determined primarily by the order of the input tuples from which
they were derived, and secondarily by the order in which their
start items appear in the binding sequence. If ordering mode is
unordered, the order of tuples in the output stream is
implementation-dependent.

The following example illustrates a window clause
that is the initial clause in a FLWOR expression. The example is
based on input data that consists of a sequence of closing stock
prices for a specific company. For this example we assume the
following input data (assume that the price elements
have a validated type of xs:decimal):

A user wishes to find "run-ups," which are defined as sequences
of dates that begin with a "low" and end with a "high" price (that
is, the stock price begins to rise on the first day of the run-up,
and continues to rise or remain even through the last day of the
run-up.) The following query uses a tumbling window to find run-ups
in the input data:

For our sample input data, this tumbling window
clause generates a tuple stream consisting of two tuples, each
representing a window and containing five bound variables named
$w, $first, $second,
$last, and $beyond. The
return clause is evaluated for each of these tuples,
generating the following query result:

The following example illustrates a window clause
that is an intermediate clause in a FLWOR expression. In this
example, the input data contains closing stock prices for several
different companies, each identified by a three-letter symbol. We
assume the following input data (again assuming that the type of
the price element is xs:decimal):

As in the previous example, we want to find "run-ups," which are
defined as sequences of dates that begin with a "low" and end with
a "high" price for a specific company. In this example, however,
the input data consists of stock prices for multiple companies.
Therefore it is necessary to isolate the stock prices of each
company before forming windows. This can be accomplished by an
initial for and let clause, followed by a
window clause, as follows:

The for and let clauses in this query
generate an initial tuple stream consisting of two tuples. In the
first tuple, $symbol is bound to "ABC" and
$closings is bound to the sequence of
closing elements for company ABC. In the second tuple,
$symbol is bound to "DEF" and $closings
is bound to the sequence of closing elements for
company DEF.

The window clause operates on this initial tuple
stream, generating two windows for the first tuple and two windows
for the second tuple. The result is a tuple stream consisting of
four tuples, each with the following bound variables:
$symbol, $closings, $w,
$first, $second, $last, and
$beyond. The return clause is then
evaluated for each of these tuples, generating the following query
result:

3.8.5 Where Clause

A where clause serves as a filter for the tuples in
its input tuple stream. The expression in the where
clause, called the where-expression, is evaluated once for
each of these tuples. If the effective boolean value of the where-expression
is true, the tuple is retained in the output tuple
stream; otherwise the tuple is discarded.

Examples:

This example illustrates the effect of a where
clause on a tuple stream:

3.8.6 Count Clause

The purpose of a count clause is to enhance the
tuple stream with a new variable that is bound, in each tuple, to
the ordinal position of that tuple in the tuple stream. The name of
the new variable is specified in the count clause.

The output tuple stream of a count clause is the
same as its input tuple stream, with each tuple enhanced by one
additional variable that is bound to the ordinal position of that
tuple in the tuple stream. However, if the name of the new variable
is the same as the name of an existing variable in the input tuple
stream, the new variable occludes (replaces) the existing variable
of the same name, and the number of bound variables in each tuple
is unchanged.

The following examples illustrate uses of the count
clause:

This example illustrates the effect of a count
clause on an input tuple stream:

This example illustrates how a counter might be used to filter
the result of a query. The query ranks products in order by
decreasing sales, and returns the three products with the highest
sales. Assume that the variable $products is bound to
a sequence of product elements, each of which has
name and sales child-elements.

3.8.7 Group By
Clause

A group by clause generates an output tuple stream
in which each tuple represents a group of tuples from the input
tuple stream. We will refer to the tuples in the input tuple stream
as pre-grouping tuples, and the tuples in the output tuple
stream as post-grouping tuples.

The post-grouping tuples have exactly the same variable-names as
the pre-grouping tuples. The number of post-grouping tuples is less
than or equal to the number of pre-grouping tuples. The group
by clause assigns each pre-grouping tuple to a group, and
generates one post-grouping tuple for each group. Subsequent
clauses in the FLWOR expression see only the variable bindings in
the post-grouping tuples; they no longer have access to the
variable bindings in the pre-grouping tuples.

[Definition: A group by
clause consists of the keywords group by followed by
one or more variables called grouping variables.] The name
of each grouping variable must be equal (by the eq
operator on expanded QNames) to the name of a bound variable in the
input tuple stream; otherwise a static error is raised [err:XQST0094].

[Definition: Equivalence
of two atomic valuesV1 and V2 is defined by
the following equivalence rules:

The input tuple stream is partitioned into groups of tuples
whose grouping
keys are equivalent. Two tuples T1 and
T2 are in the same group if and only if, for each
grouping
variableGV, the atomized value of GV in
T1 is equivalent to the atomized value of
GV in T2.

Each group of tuples produced by the above process results in
one post-grouping tuple. The pre-grouping tuples from which the
group is derived have equivalentgrouping keys, but these keys are not
necessarily identical (for example, the strings "Frog" and "frog"
might be equivalent according to the collation in use.) In
the post-grouping tuple, each grouping variable is bound to the value
of one of the original grouping variables. The choice of which
grouping
variable is chosen is implementation-dependent.

Editorial
note

Some members of the
XQuery Working Group would prefer that the grouping variables in
the post-grouping tuple contain the grouping key for a grouping
variable in a pre-grouping tuple, which is atomized, rather than
the value of the grouping variable in a pre-grouping tuple. We
welcome feedback on this question.

In the post-grouping tuple generated for a given group, each
non-grouping variable is bound to a sequence containing the
concatenated values of that variable in all the pre-grouping tuples
that were assigned to that group. If ordering mode is ordered, the
values derived from individual tuples are concatenated in a way
that preserves the order of the pre-grouping tuple stream;
otherwise the ordering of these values is implementation-dependent.

Note:

This behavior may be surprising to SQL programmers, since SQL
reduces the equivalent of a non-grouping variable to one
representative value. Consider the following query:

let $x := 64000
for $c in //customer
let $d := $c/department
where $c/salary > $x
group by $d
return
<department name="{$d}">
Number of employees earning more than ${$x} is {count($c)}
</department>

If there are three qualifying customers in the sales department
this evaluates to:

<department name="sales">
Number of employees earning more than $64000 64000 64000 is 3
</department>

In XQuery, each group is a sequence of items that match the
group by criteria—in a tree-structured language like XQuery, this
is convenient, because further structures can be built based on the
items in this sequence. Because there are three items in the group,
$x evaluates to a sequence of three items. To reduce
this to one item, use fn:distinct-values():

let $x := 64000
for $c in //customer
let $d := $c/department
where $c/salary > $x
group by $d
return
<department name="{$d}">
Number of employees earning more than ${distinct-values($x)} is {count($c)}
</department>

Note:

In general, the static type of a variable in a post-grouping
tuple is different from the static type of the variable with the same
name in the pre-grouping tuples.

An order by clause can be used to impose a
value-based ordering on the post-grouping tuple stream. Similarly,
if it is desired to impose a value-based ordering within a group
(i.e., on the sequence of items bound to a non-grouping variable),
this can be accomplished by a nested FLWOR expression that iterates
over these items and applies an order by clause. In
some cases, a value-based ordering within groups can be
accomplished by applying an order by clause on a
non-grouping variable before applying the group by
clause.

A group by clause rebinds all the variables in the
input tuple stream. The scopes of these variables are not affected
by the group by clause, but in post-grouping tuples
the values of the variables represent group properties rather than
properties of individual pre-grouping tuples.

Examples:

This example illustrates the effect of a group by
clause on a tuple stream.

This example and the ones that follow are based on two separate
sequences of elements, named $sales and
$products. We assume that the variable
$sales is bound to a sequence of elements with the
following structure:

In a more realistic example, a user might be interested in the
total revenue generated by each store for each product category.
Revenue depends on both the quantity sold of various items and the
price of each item. The following query joins the two input
sequences and groups the resulting tuples by two grouping
variables:

The result of the previous example was a "flat" list of
elements. A user might prefer the query result to be presented in
the form of a hierarchical report, grouped primarily by store (in
order by store number) and secondarily by product category. Within
each store, the user might want to see only those product
categories whose total revenue exceeds $10,000, presented in
descending order by their total revenue. This report is generated
by the following query:

When writing a query that includes a group by
clause, it is important to remember that, in each post-grouping
tuple, each grouping variable is bound to a single
atomic value (a grouping key), and all other variables are
bound to sequences of items derived from all the pre-grouping
tuples from which the group was formed. The following example
illustrates how to avoid a possible pitfall in writing grouping
queries.

The repetition of "1000" in this query result is due to the fact
that $high-price is not a grouping variable. One way to
avoid this repetition is to move the binding of
$high-price to an outer-level FLWOR expression, as
follows:

The purpose of an order by clause is to impose a
value-based ordering on the tuples in the tuple stream. The output
tuple stream of the order by clause contains the same
tuples as its input tuple stream, but the tuples may be in a
different order.

An order by clause contains one or more ordering
specifications, called orderspecs, as shown in the grammar.
For each tuple in the input tuple stream, the orderspecs are
evaluated, using the variable bindings in that tuple. The relative
order of two tuples is determined by comparing the values of their
orderspecs, working from left to right until a pair of unequal
values is encountered. If an orderspec specifies a collation, that collation is
used in comparing values of type xs:string,
xs:anyURI, or types derived from them (otherwise, the
default
collation is used in comparing values of these types). If an
orderspec specifies a collation by a relative URI, that relative
URI is resolved to an absolute URI using the base URI in the static context. If an orderspec
specifies a collation that is not found in statically known collations, an error
is raised [err:XQST0076].

The process of evaluating and comparing the orderspecs is based
on the following rules:

Atomization is
applied to the result of the expression in each orderspec. If the
result of atomization is neither a single atomic value nor an empty
sequence, a type
error is raised [err:XPTY0004].

If the value of an orderspec has the dynamic typexs:untypedAtomic (such as character data in a
schemaless document), it is cast to the type
xs:string.

Note:

Consistently treating untyped values as strings enables the
sorting process to begin without complete knowledge of the types of
all the values to be sorted.

All the non-empty orderspec values must be convertible to a
common type by subtype substitution and/or
type
promotion. The ordering is performed in the least common type
that has a gt operator. If two or more non-empty
orderspec values are not convertible to a common type that has a
gt operator, a type error is raised [err:XPTY0004].

Example: The orderspec values include a value of type
hatsize, which is derived from
xs:integer, and a value of type shoesize,
which is derived from xs:decimal. The least common
type reachable by subtype substitution and type promotion is
xs:decimal.

Example: The orderspec values include a value of type
xs:string and a value of type xs:anyURI.
The least common type reachable by subtype substitution and type
promotion is xs:string.

For the purpose of determining their relative position in the
ordering sequence, the greater-than relationship between
two orderspec values W and V is defined as
follows:

When the orderspec specifies empty least, the
following rules are applied in order:

If V is an empty sequence and W is not an
empty sequence, then Wgreater-thanV is
true.

If V is NaN and W is neither
NaN nor an empty sequence, then Wgreater-thanV is true.

If T1 and T2 are two tuples in the input tuple
stream, and V1 and V2 are the first pair of
values encountered when evaluating their orderspecs from left to
right for which one value is greater-than the other (as
defined above), then:

If V1 is greater-thanV2: If the
orderspec specifies descending, then T1
precedes T2 in the output tuple stream; otherwise,
T2 precedes T1 in the output tuple stream.

If V2 is greater-thanV1: If the
orderspec specifies descending, then T2
precedes T1 in the output tuple stream; otherwise,
T1 precedes T2 in the output tuple stream.

If neither V1 nor V2 is greater-than
the other for any pair of orderspecs for tuples T1 and
T2, the following rules apply.

If stable is specified, the original order of
T1 and T2 is preserved in the output tuple
stream.

If two orderspecs return the special floating-point values
positive and negative zero, neither of these values is
greater-than the other, since +0.0 gt -0.0
and -0.0 gt +0.0 are both false.

Examples:

This example illustrates the effect of an order by
clause on a tuple stream. The keyword stable indicates
that, when two tuples have equal sort keys, their order in the
input tuple stream is preserved.

The following example shows how an order by clause
can be used to sort the result of a query, even if the sort key is
not included in the query result. This query returns employee names
in descending order by salary, without returning the actual
salaries:

for $e in $employees
order by $e/salary descending
return $e/name

Note:

Since the order by clause in a FLWOR expression is
the only facility provided by XQuery for specifying a value
ordering, a FLWOR expression must be used in some queries where
iteration would not otherwise be necessary. For example, a list of
books with price less than 100 might be obtained by a simple
path
expression such as $books/book[price < 100].
But if these books are to be returned in alphabetic order by title,
the query must be expressed as follows:

for $b in $books/book[price < 100]
order by $b/title
return $b

3.8.9
Return Clause

The return clause is the final clause of a FLWOR
expression. The return clause is evaluated once for
each tuple in its input tuple stream, using the variable bindings
in the respective tuples, in the order in which these tuples appear
in the input tuple stream. The results of these evaluations are
concatenated, as if by the comma operator, to form the result of the
FLWOR expression.

The following example illustrates a FLWOR expression containing
several clauses. The for clause iterates over all the
departments in an input document named depts.xml,
binding the variable $d to each department in turn.
For each binding of $d, the let clause
binds variable $e to all the employees in the given
department, selected from another input document named
emps.xml (the relationship between employees and
departments is represented by matching their deptno
values). Each tuple in the resulting tuple stream contains a pair
of bindings for $d and $e
($d is bound to a department and $e is
bound to a set of employees in that department). The
where clause filters the tuple stream, retaining only
those tuples that represent departments having at least ten
employees. The order by clause orders the surviving
tuples in descending order by the average salary of the employees
in the department. The return clause constructs a new
big-dept element for each surviving tuple, containing
the department number, headcount, and average salary.

The order in which items appear in the result of a FLWOR
expression depends on the ordering of the input tuple stream to the
return clause, which in turn is influenced by
order by clauses and by ordering mode. For example, consider the
following query, which is based on the same two input documents as
the previous example:

for $d in fn:doc("depts.xml")//dept
order by $d/deptno
for $e in fn:doc("emps.xml")//emp[deptno eq $d/deptno]
return
<assignment>
{$d/deptno, $e/name}
</assignment>

The result of this query is a sequence of
assignment elements, each containing a
deptno element and a name element. The
sequence will be ordered primarily by the deptno
values because of the order by clause. If ordering mode is
ordered, subsequences of assignment
elements with equal deptno values will be ordered by
the document order of their name elements within the
emps.xml document; otherwise the ordering of these
subsequences will be implementation-dependent.

Parentheses are helpful in return clauses that
contain comma operators, since FLWOR expressions have a higher
precedence than the comma operator. For example, the following
query raises an error because after the comma, $j is
no longer within the FLWOR expression, and is an undefined
variable:

let $i := 5,
$j := 20 * $i
return $i, $j

Parentheses can be used to bring $j into the
return clause of the FLWOR expression, as the
programmer probably intended:

let $i := 5,
$j := 20 * $i
return ($i, $j)

3.9 Ordered and Unordered
Expressions

The purpose of ordered and unordered
expressions is to set the ordering mode in the static context to
ordered or unordered for a certain region
in a query. The specified ordering mode applies to the expression
nested inside the curly braces. For expressions where the ordering
of the result is not significant, a performance advantage may be
realized by setting the ordering mode to unordered,
thereby granting the system flexibility to return the result in the
order that it finds most efficient.

In a region of a query where ordering mode is
unordered, the result of an expression may be
nondeterministic if the expression invokes certain functions that
are affected by the ordering of node sequences. These functions
include fn:position, fn:last,
fn:index-of, fn:insert-before,
fn:remove, fn:reverse, and
fn:subsequence. Also, within a path expression in
an unordered region, numeric predicates are
nondeterministic. For example, in an ordered region, the path
expression (//a/b)[5] will return the fifth qualifying
b-element in document order. In an unordered region,
the same expression will return an implementation-dependent
qualifying b-element.

Note:

The fn:id and fn:idref functions are
described in [XQuery and XPath
Functions and Operators 1.1] as returning their results in
document
order. Since ordering mode is a feature of XQuery, relaxation
of the ordering requirement for function results when ordering mode
is unordered is a feature of XQuery rather than of the
functions themselves.

The use of an unordered expression is illustrated
by the following example, which joins together two documents named
parts.xml and suppliers.xml. The example
returns the part numbers of red parts, paired with the supplier
numbers of suppliers who supply these parts. If an
unordered expression were not used, the resulting list
of (part number, supplier number) pairs would be required to have
an ordering that is controlled primarily by the document order of
parts.xml and secondarily by the document order of
suppliers.xml. However, this might not be the most
efficient way to process the query if the ordering of the result is
not important. An XQuery implementation might be able to process
the query more efficiently by using an index to find the red parts,
or by using suppliers.xml rather than
parts.xml to control the primary ordering of the
result. The unordered expression gives the query
evaluator freedom to make these kinds of optimizations.

In addition to ordered and unordered
expressions, XQuery provides a function named
fn:unordered that operates on any sequence of items
and returns the same sequence in a nondeterministic order. A call
to the fn:unordered function may be thought of as
giving permission for the argument expression to be materialized in
whatever order the system finds most efficient. The
fn:unordered function relaxes ordering only for the
sequence that is its immediate operand, whereas an
unordered expression sets the ordering mode for its operand
expression and all nested expressions.

3.10
Conditional Expressions

XQuery 1.1 supports a conditional expression based on the
keywords if, then, and
else.

The value of a conditional expression is defined as follows: If
the effective boolean value of the test expression is
true, the value of the then-expression is returned. If
the effective boolean value of the test expression is
false, the value of the else-expression is
returned.

Conditional expressions have a special rule for propagating
dynamic
errors. If the effective value of the test expression is
true, the conditional expression ignores (does not
raise) any dynamic errors encountered in the else-expression. In
this case, since the else-expression can have no observable effect,
it need not be evaluated. Similarly, if the effective value of the
test expression is false, the conditional expression
ignores any dynamic errors encountered in the
then-expression, and the then-expression need not be evaluated.

3.11 Switch
Expression

The switch expression chooses one of several expressions
to evaluate based on the input value.

In a switch expression, the switch
keyword is followed by an expression enclosed in parentheses,
called the switch operand expression. This is the expression
whose value is being compared. The remainder of the
switch expression consists of one or more
case clauses, with one or more case operand
expressions each, and a default clause.

The first step in evaluating a switch expression is to apply
atomization to the value of the switch operand expression. If the
result is a sequence of length greater than one, a type error is
raised [err:XPTY0004]. If the atomized operand is of
type xs:untypedAtomic, it is cast to xs:string.

[Definition: The effective
case in a switch expression is the first case clause in which
the value of the switch operand expression is equivalent to the
value of a case operand, as defined in equivalence of two atomic
values, or the default clause if no such case clause exists.]
The value of the switch expression is the value of the return
expression in the effective case.

A special rule applies to propagation of dynamic errors by
switch expressions. The case clauses of a switch expression do not
raise any dynamic errors except in the effective case. Dynamic
errors raised in the operand expressions of the switch or the case
clauses are propagated. An implementation must not raise errors in
the operand expressions of case clauses that occur after the
effective case.

A quantified expression begins with a quantifier,
which is the keyword some or every,
followed by one or more in-clauses that are used to bind variables,
followed by the keyword satisfies and a test
expression. Each in-clause associates a variable with an expression
that returns a sequence of items, called the binding sequence for
that variable. The in-clauses generate tuples of variable bindings,
including a tuple for each combination of items in the binding
sequences of the respective variables. Conceptually, the test
expression is evaluated for each tuple of variable bindings.
Results depend on the effective boolean value of the test expressions, as
defined in 2.4.3 Effective Boolean
Value. The value of the quantified expression is defined by
the following rules:

If the quantifier is some, the quantified
expression is true if at least one evaluation of the
test expression has the effective boolean valuetrue; otherwise
the quantified expression is false. This rule implies
that, if the in-clauses generate zero binding tuples, the value of
the quantified expression is false.

If the quantifier is every, the quantified
expression is true if every evaluation of the test
expression has the effective boolean valuetrue; otherwise
the quantified expression is false. This rule implies
that, if the in-clauses generate zero binding tuples, the value of
the quantified expression is true.

The scope of a variable bound in a quantified expression
comprises all subexpressions of the quantified expression that
appear after the variable binding. The scope does not include the
expression to which the variable is bound.

The order in which test expressions are evaluated for the
various binding tuples is implementation-dependent. If the
quantifier is some, an implementation may return
true as soon as it finds one binding tuple for which
the test expression has an effective boolean value of true, and it
may raise a dynamic error as soon as it finds one
binding tuple for which the test expression raises an error.
Similarly, if the quantifier is every, an
implementation may return false as soon as it finds
one binding tuple for which the test expression has an effective boolean
value of false, and it may raise a dynamic error as soon
as it finds one binding tuple for which the test expression raises
an error. As a result of these rules, the value of a quantified
expression is not deterministic in the presence of errors, as
illustrated in the examples below.

Here are some examples of quantified expressions:

This expression is true if every part
element has a discounted attribute (regardless of the
values of these attributes):

every $part in /parts/part satisfies $part/@discounted

This expression is true if at least one
employee element satisfies the given comparison
expression:

In the following examples, each quantified expression evaluates
its test expression over nine tuples of variable bindings, formed
from the Cartesian product of the sequences (1, 2, 3)
and (2, 3, 4). The expression beginning with
some evaluates to true, and the
expression beginning with every evaluates to
false.

some $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4

every $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4

This quantified expression may either return true
or raise a type
error, since its test expression returns true for
one variable binding and raises a type error for another:

some $x in (1, 2, "cat") satisfies $x * 2 = 4

This quantified expression may either return false
or raise a type
error, since its test expression returns false for
one variable binding and raises a type error for another:

3.13 Try/Catch
Expressions

The try/catch expression provides error handling for dynamic
errors and type errors raised during dynamic evaluation, including
errors raised by the XQuery implementation and errors explicitly
raised in a query using the fn:error() function.

A try/catch expression catches dynamic errors and type errors raised during dynamic
evaluation for expressions that are lexically contained within the
try clause. If the target expression does not raise a
dynamic error or a type error, the result of the try/catch
expression is the result of the target expression.

If the target expression raises a dynamic error or a type error,
the result of the try/catch expression is obtained by evaluating
the first catch clause that "matches" the error value,
as described below. A catch clause with one or more
NameTests matches any error whose error code matches one of these
NameTests. For instance, if the error code is
err:FOER0000, then it matches a catch
clause whose ErrorList is err:FOER0000 | err:FOER0001.
Wildcards may be used in NameTests; thus, the error code
err:FOER0000 also matches a catch clause
whose ErrorList is err:* or *:FOER0000 or
*.

If an error is matched, the optional variables in the
catch clause are bound, in order, to the error's code,
description, and value. These variables are then in scope in the
catch clause. The types of these variables match the
types of the corresponding parameters in the error()
function: ErrorCode has type xs:QName,
ErrorDescr has type xs:string?, and
ErrorVal has type item()*. If no
catch clause matches an error, the try/catch
expression raises that error. If an error is raised in a catch
clause, the try/catch expression raises that error.

If an error found in a try clause can be detected
statically, an implementation is free to raise a static error.
Static errors are not caught by the try/catch expression.

If a function call occurs within a try clause,
errors raised by evaluating the corresponding function are caught
by the try/catch expression. If a variable reference is used in a
try clause, errors raised by binding a value to the
variable are not caught unless the binding expression occurs within
the try clause.

Note:

The presence of a try/catch expression does not prevent an
implementation from using a lazy evaluation strategy, nor does it
prevent an optimizer performing expression rewrites. However, if
the evaluation of an expression inside a try/catch is rewritten or
deferred in this way, it must take its try/catch context with it.
Similarly, expressions that were written outside the try/catch
expression may be evaluated inside the try/catch, but only if they
retain their original try/catch behavior. The presence of a
try/catch does not change the rules that allow the processor to
evaluate expressions in such a way that may avoid the detection of
some errors.

Here are some examples of try/catch expressions.

A try/catch expression without a CatchErrorList catches any
error:

try {
$x cast as xs:integer
}
catch * {
0
}

The CatchErrorList in this try/catch expression specifies that
only err:FORG0001 is caught:

try {
$x cast as xs:integer
}
catch err:FORG0001 {
0
}

The CatchErrorList in this try/catch expression specifies that
errors err:FORG0001 and err:XPTY0004 are
caught:

try {
$x cast as xs:integer
}
catch err:FORG0001 | err:XPTY0004 {
0
}

Note:

In some implementations, err:XPTY0004 is detected
during static evaluation; it can only be caught if it is raised
during dynamic evaluation.

This try/catch expression shows how to bind variables to the
error code, error description, and error value. Since the
CatchErrorList is a wildcard, it catches any error:

3.14.1
Instance Of

The boolean operator instance of returns
true if the value of its first operand matches the
SequenceType in its second
operand, according to the rules for SequenceType matching; otherwise it
returns false. For example:

5 instance of xs:integer

This example returns true because the given value
is an instance of the given type.

5 instance of xs:decimal

This example returns true because the given value
is an integer literal, and xs:integer is derived by
restriction from xs:decimal.

<a>{5}</a> instance of xs:integer

This example returns false because the given value
is an element rather than an integer.

(5, 6) instance of xs:integer+

This example returns true because the given
sequence contains two integers, and is a valid instance of the
specified type.

. instance of element()

This example returns true if the context item is an
element node or false if the context item is defined
but is not an element node. If the context item is undefined, a
dynamic error
is raised [err:XPDY0002].

3.14.2
Typeswitch

The typeswitch expression chooses one of
several expressions to evaluate based on the dynamic type of an input
value.

In a typeswitch expression, the
typeswitch keyword is followed by an expression
enclosed in parentheses, called the operand expression. This
is the expression whose type is being tested. The remainder of the
typeswitch expression consists of one or more
case clauses and a default clause.

Each case clause specifies a
SequenceType followed by a
return expression. [Definition: The
effective case in a typeswitch expression is
the first case clause such that the value of the
operand expression matches the SequenceType in the
case clause, using the rules of SequenceType matching.] The value
of the typeswitch expression is the value of the
return expression in the effective case. If the value
of the operand expression does not match any SequenceType named in a
case clause, the value of the typeswitch
expression is the value of the return expression in
the default clause.

In a case or default clause, if the
value to be returned depends on the value of the operand
expression, the clause must specify a variable name. Within the
return expression of the case or
default clause, this variable name is bound to the
value of the operand expression. Inside a case clause,
the static type
of the variable is the SequenceType named in the
case clause. Inside a default clause, the
static type of the variable is the same as the static type of the
operand expression. If the value to be returned by a
case or default clause does not depend on
the value of the operand expression, the clause need not specify a
variable.

The scope of a variable binding in a case or
default clause comprises that clause. It is not an
error for more than one case or default
clause in the same typeswitch expression to bind
variables with the same name.

A special rule applies to propagation of dynamic errors by
typeswitch expressions. A typeswitch
expression ignores (does not raise) any dynamic errors encountered
in case clauses other than the effective case.
Dynamic errors encountered in the default clause are
raised only if there is no effective case.

The following example shows how a
typeswitch expression might be used to process an
expression in a way that depends on its dynamic type.

3.14.3 Cast

Occasionally it is necessary to convert a value to a specific
datatype. For this purpose, XQuery 1.1 provides a cast
expression that creates a new value of a specific type based on an
existing value. A cast expression takes two operands:
an input expression and a target type. The type of
the input expression is called the input type. The target
type must be an atomic type that is in the in-scope schema
types [err:XPST0051]. In addition, the target type
cannot be xs:NOTATION or xs:anyAtomicType
[err:XPST0080]. The
optional occurrence indicator "?" denotes that an
empty sequence is permitted. If the target type has no namespace
prefix, it is considered to be in the default
element/type namespace. The semantics of the cast
expression are as follows:

If the result of atomization is a single atomic value, the
result of the cast expression depends on the input type and the
target type. In general, the cast expression attempts to create a
new value of the target type based on the input value. Only certain
combinations of input type and target type are supported. A summary
of the rules are listed below—the normative definition of these
rules is given in [XQuery and XPath
Functions and Operators 1.1]. For the purpose of these rules,
an implementation may determine that one type is derived by
restriction from another type either by examining the in-scope schema
definitions or by using an alternative, implementation-dependent
mechanism such as a data dictionary.

If the target type of a cast expression is
xs:QName, or is a type that is derived from
xs:QName or xs:NOTATION, and if the base
type of the input is not the same as the base type of the target
type, then the input expression must be a string literal [err:XPTY0004].

Note:

The reason for this rule is that construction of an instance of
one of these target types from a string requires knowledge about
namespace bindings. If the input expression is a non-literal
string, it might be derived from an input document whose namespace
bindings are different from the statically known namespaces.

cast is supported if the input type is a
non-primitive atomic type that is derived by restriction from the
target type. In this case, the input value is mapped into the value
space of the target type, unchanged except for its type. For
example, if shoesize is derived by restriction from
xs:integer, a value of type shoesize can
be cast into the schema type xs:integer.

cast is supported if the target type is a
non-primitive atomic type and the input type is
xs:string or xs:untypedAtomic. The input
value is first converted to a value in the lexical space of the
target type by applying the whitespace normalization rules for the
target type (as defined in [XML Schema]).
The lexical value is then converted to the value space of the
target type using the schema-defined rules for the target type. If
the input value fails to satisfy some facet of the target type, a
dynamic error
may be raised as specified in [XQuery
and XPath Functions and Operators 1.1].

cast is supported if the target type is a
non-primitive atomic type that is derived by restriction from the
input type. The input value must satisfy all the facets of the
target type (in the case of the pattern facet, this is checked by
generating a string representation of the input value, using the
rules for casting to xs:string). The resulting value
is the same as the input value, but with a different dynamic type.

If a primitive type P1 can be cast into a primitive type P2,
then any type derived by restriction from P1 can be cast into any
type derived by restriction from P2, provided that the facets of
the target type are satisfied. First the input value is cast to P1
using rule (b) above. Next, the value of type P1 is cast to the
type P2, using rule (a) above. Finally, the value of type P2 is
cast to the target type, using rule (d) above.

For any combination of input type and target type that is not in
the above list, a cast expression raises a type error [err:XPTY0004].

If casting from the input type to the target type is supported
but nevertheless it is not possible to cast the input value into
the value space of the target type, a dynamic error is raised.
[err:FORG0001] This includes the case when any facet of the target
type is not satisfied. For example, the expression
"2003-02-31" cast as xs:date would raise a dynamic error.

3.14.4 Castable

XQuery 1.1 provides an expression that tests whether a given
value is castable into a given target type. The target type must be
an atomic type that is in the in-scope schema types [err:XPST0051]. In addition, the target type
cannot be xs:NOTATION or xs:anyAtomicType
[err:XPST0080]. The
optional occurrence indicator "?" denotes that an
empty sequence is permitted.

The expression E castable as T returns
true if the result of evaluating E can be
successfully cast into the target type T by using a
cast expression; otherwise it returns
false. If evaluation of E fails with a
dynamic error, the castable expression as a whole
fails. The castable expression can be used as a
predicate to avoid
errors at evaluation time. It can also be used to select an
appropriate type for processing of a given value, as illustrated in
the following example:

if ($x castable as hatsize)
then $x cast as hatsize
else if ($x castable as IQ)
then $x cast as IQ
else $x cast as xs:string

Note:

If the target type of a castable expression is
xs:QName, or is a type that is derived from
xs:QName or xs:NOTATION, and the input
argument of the expression is of type xs:string but it
is not a literal string, the result of the castable
expression is false.

3.14.5 Constructor Functions

For every atomic type in the in-scope schema types (except
xs:NOTATION and xs:anyAtomicType, which
are not instantiable), a constructor function is implicitly
defined. In each case, the name of the constructor function is the
same as the name of its target type (including namespace). The
signature of the constructor function for type T is as
follows:

T($arg as xs:anyAtomicType?) as T?

[Definition: The constructor
function for a given type is used to convert instances of other
atomic types into the given type. The semantics of the constructor
function call T($arg) are defined to be equivalent to
the expression (($arg) cast as T?).]

The constructor functions for xs:QName and for
types derived from xs:QName and
xs:NOTATION require their arguments to be string
literals or to have a base type that is the same as the base type
of the target type; otherwise a type error [err:XPTY0004] is raised. This rule is
consistent with the semantics of cast expressions for
these types, as defined in 3.14.3
Cast.

The following examples illustrate the use of constructor
functions:

This example is equivalent to ("2000-01-01" cast as
xs:date?).

xs:date("2000-01-01")

This example is equivalent to (($floatvalue * 0.2E-5) cast
as xs:decimal?).

xs:decimal($floatvalue * 0.2E-5)

This example returns a xs:dayTimeDuration value
equal to 21 days. It is equivalent to ("P21D" cast as
xs:dayTimeDuration?).

xs:dayTimeDuration("P21D")

If usa:zipcode is a user-defined atomic type in the
in-scope schema
types, then the following expression is equivalent to the
expression ("12345" cast as usa:zipcode?).

usa:zipcode("12345")

Note:

An instance of an atomic type that is not in a namespace can be
constructed in either of the following ways:

3.14.6 Treat

XQuery 1.1 provides an expression called treat that
can be used to modify the static type of its operand.

Like cast, the treat expression takes
two operands: an expression and a SequenceType. Unlike
cast, however, treat does not change the
dynamic type or
value of its operand. Instead, the purpose of treat is
to ensure that an expression has an expected dynamic type at
evaluation time.

The semantics of expr1treat
astype1 are as follows:

During static analysis:

The static
type of the treat expression is
type1 . This enables the expression to be
used as an argument of a function that requires a parameter of
type1 .

During expression evaluation:

If expr1 matches
type1 , using the rules for SequenceType matching, the
treat expression returns the value of
expr1 ; otherwise, it raises a dynamic error
[err:XPDY0050]. If
the value of expr1 is returned, its identity
is preserved. The treat expression ensures that the
value of its expression operand conforms to the expected type at
run-time.

Example:

$myaddress treat as element(*, USAddress)

The static
type of $myaddress may be element(*,
Address), a less specific type than element(*,
USAddress). However, at run-time, the value of
$myaddress must match the type element(*,
USAddress) using rules for SequenceType matching;
otherwise a dynamic error is raised [err:XPDY0050].

3.15 Validate
Expressions

A validate expression can be used to validate a
document node or an element node with respect to the in-scope schema
definitions, using the schema validation process defined in
[XML Schema]. If the operand of a
validate expression does not evaluate to exactly one
document or element node, a type error is raised [err:XQTY0030]. In this specification, the
node that is the operand of a validate expression is
called the operand node.

A validate expression returns a new node with its
own identity and with no parent. The new node and its descendants
are given type annotations that are generated by
applying a validation process to the operand node. In some cases,
default values may also be generated by the validation process.

The result of a validate expression is defined by
the following rules.

If the operand node is a document node, its children must
consist of exactly one element node and zero or more comment and
processing instruction nodes, in any order; otherwise, a dynamic error
[err:XQDY0061] is
raised.

If a type name is provided, schema-validity assessment is
carried out according to the rules defined in [XML Schema], section 3.3.4 "Element Declaration
Validation Rules", clauses 1.2 and 2, using this type definition as
the "processor-stipulated type definition" for validation.

Validity assessment is carried out on the root element
information item of the resulting Infoset, using the in-scope schema
definitions as the effective schema. The process of validation
applies recursively to contained elements and attributes to the
extent required by the effective schema. During validity
assessment, the following special rules are in effect:

If validation mode is
strict, then there must be a top-level element
declaration in the in-scope element declarations that matches the
root element information item in the Infoset, and schema-validity
assessment is carried out using that declaration in accordance with
item 2 of [XML Schema] Part 1, section
5.2, "Assessing Schema-Validity." If there is no such element
declaration, a dynamic error is raised [err:XQDY0084].

If validation mode is
lax, then schema-validity assessment is carried out in
accordance with item 3 of [XML Schema]
Part 1, section 5.2, "Assessing Schema-Validity."

If validation mode is
lax and the root element information item has neither
a top-level element declaration nor an xsi:type
attribute, [XML Schema] defines the
recursive checking of children and attributes as optional. During
processing of an XQuery validate expression, this
recursive checking is required.

If the operand node is an element node, the validation rules
named "Validation Root Valid (ID/IDREF)" is not applied. This means
that document-level constraints relating to uniqueness and
referential integrity are not enforced.

There is no check that the document contains unparsed entities
whose names match the values of nodes of type
xs:ENTITY or xs:ENTITIES.

There is no check that the document contains notations whose
names match the values of nodes of type
xs:NOTATION.

Note:

Validity assessment is affected by the presence or absence of
xsi:type attributes on the elements being validated,
and may generate new information items such as default
attributes.

The next step depends on validation mode and on the
validity property of the root element information item
in the PSVI that results from the validation process.

If the validity property of the root element
information item is valid, or if validation mode is
lax and the validity property of the root
element information item is notKnown, the PSVI is
converted back into an XDM instance as described in [XQuery and XPath Data Model (XDM) 1.1]
Section 3.3, "Construction from a PSVI". The resulting node (a new
node of the same kind as the operand node) is returned as the
result of the validate expression.

The effect of these rules is as follows: If validation mode is
strict, the validated element must have a top-level
element declaration in the effective schema, and must conform to
this declaration. If validation mode is
lax, the validated element must conform to its
top-level element declaration if such a declaration exists in the
effective schema. If validation mode is
lax and there is no top-level element declaration for
the element, and the element has an xsi:type
attribute, then the xsi:type attribute must name a
top-level type definition in the effective schema, and the element
must conform to that type. The validated element corresponds either
to the operand node or (if the operand node is a document node) to
its element child.

3.16 Extension Expressions

[Definition: An extension
expression is an expression whose semantics are implementation-defined.] Typically
a particular extension will be recognized by some implementations
and not by others. The syntax is designed so that extension
expressions can be successfully parsed by all implementations, and
so that fallback behavior can be defined for implementations that
do not recognize a particular extension.

An extension expression consists of one or more pragmas,
followed by an expression enclosed in curly braces. [Definition: A
pragma is denoted by the delimiters (# and
#), and consists of an identifying QName followed by
implementation-defined content.]
The content of a pragma may consist of any string of characters
that does not contain the ending delimiter #). The
QName of a pragma must resolve to a namespace URI and local name,
using the statically known namespaces [err:XPST0081].

Note:

Since there is no default namespace for pragmas, a pragma QName
must include a namespace prefix.

If the namespace part of a pragma QName is not recognized by the
implementation as a pragma namespace, then the pragma is ignored.
If all the pragmas in an ExtensionExpr are ignored, then
the value of the ExtensionExpr is the value of the
expression enclosed in curly braces; if this expression is absent,
then a static
error is raised [err:XQST0079].

If an implementation recognizes the namespace of one or more
pragmas in an ExtensionExpr, then the value of
the ExtensionExpr,
including its error behavior, is implementation-defined. For
example, an implementation that recognizes the namespace of a
pragma QName, but does not recognize the local part of the QName,
might choose either to raise an error or to ignore the pragma.

It is a static
error [err:XQST0013] if an implementation recognizes a
pragma but determines that its content is invalid.

If an implementation recognizes a pragma, it must report any
static errors in the following expression even if it will not
evaluate that expression (however, static type errors are raised
only if the Static Typing Feature is in
effect.)

Note:

The following examples illustrate three ways in which extension
expressions might be used.

A pragma can be used to furnish a hint for how to evaluate the
following expression, without actually changing the result. For
example:

An implementation that recognizes the exq:use-index
pragma might use an index to evaluate the expression that follows.
An implementation that does not recognize this pragma would
evaluate the expression in its normal way.

A pragma might be used to modify the semantics of the following
expression in ways that would not (in the absence of the pragma) be
conformant with this specification. For example, a pragma might be
used to permit comparison of xs:duration values using
implementation-defined semantics (this would normally be an error).
Such changes to the language semantics must be scoped to the
expression contained within the curly braces following the
pragma.

A pragma might contain syntactic constructs that are evaluated
in place of the following expression. In this case, the following
expression itself (if it is present) provides a fallback for use by
implementations that do not recognize the pragma. For example:

Here an implementation that recognizes the pragma will return
the result of evaluating the proprietary syntax exq:distinct
//city by @country, while an implementation that does not
recognize the pragma will instead return the result of the
expression //city[not(@country =
preceding::city/@country)]. If no fallback expression is
required, or if none is feasible, then the expression between the
curly braces may be omitted, in which case implementations that do
not recognize the pragma will raise a static error.

[Definition: A main module consists of a
Prolog followed by a
Query Body.] A query
has exactly one main module. In a main module, the Query Body can be evaluated,
and its value is the result of the query.

[Definition: A module that does not contain
a Query Body is
called a library module. A library module consists of a
module
declaration followed by a Prolog.] A library module cannot be evaluated
directly; instead, it provides function and variable declarations
that can be imported into other modules.

[Definition: A Prolog is a series of
declarations and imports that define the processing environment for
the module that contains
the Prolog.] Each declaration or import is followed by a semicolon.
A Prolog is organized into two parts.

The first part of the Prolog consists of setters, imports,
namespace declarations, and default namespace declarations.
[Definition:
Setters are declarations that set the value of some property
that affects query processing, such as construction mode, ordering
mode, or default collation.] Namespace declarations and default
namespace declarations affect the interpretation of QNames within
the query. Imports are used to import definitions from schemas and
modules. [Definition: Each imported schema or
module is identified by its target namespace, which is the
namespace of the objects (such as elements or functions) that are
defined by the schema or module.]

The second part of the Prolog consists of declarations of
variables, functions, and options. These declarations appear at the
end of the Prolog because they may be affected by declarations and
imports in the first part of the Prolog.

[Definition: The Query Body, if present,
consists of an expression that defines the result of the query.]
Evaluation of expressions is described in 3 Expressions. A module can be
evaluated only if it has a Query Body.

4.1 Version Declaration

[Definition: A version
declaration can identify the applicable XQuery syntax and
semantics for a module, as
well as its encoding.] The version number "1.0" indicates a
requirement that the module must be processed by an XQuery 1.0
processor; the version number "1.1" indicates a requirement
that the module must be processed by an XQuery 1.1
processor. If the version declaration is not present or the
version is not included in the declaration, an XQuery 1.1 processor
assumes a version of "1.1". If an XQuery 1.1 processor processes a
module labeled with a version of "1.0", it must either raise a
static error [err:XQST0031], or attempt to process the module
with an XQuery 1.0 processor. If any version number other
than 1.1 or 1.0 is encountered, a static error [err:XQST0031] is
raised.

[Definition: If present, a
version declaration may optionally include an encoding
declaration. The value of the string literal following the
keyword encoding is an encoding name, and must conform
to the definition of EncName specified in [XML 1.0] [err:XQST0087]. The purpose of an encoding
declaration is to allow the writer of a query to provide a string
that indicates how the query is encoded, such as
"UTF-8", "UTF-16", or
"US-ASCII".] Since the encoding of a query may change
as the query moves from one environment to another, there can be no
guarantee that the encoding declaration is correct.

The handling of an encoding declaration is implementation-dependent. If an
implementation has a priori knowledge of the encoding of a
query, it may use this knowledge and disregard the encoding
declaration. The semantics of a query are not affected by the
presence or absence of an encoding declaration.

4.2 Module Declaration

[Definition: A module declaration
serves to identify a module
as a library
module. A module declaration begins with the keyword
module and contains a namespace prefix and a URILiteral.] The URILiteral must be
of nonzero length [err:XQST0088]. The URILiteral identifies the
target
namespace of the library module, which is the namespace for all
variables and functions exported by the library module. The name of
every variable and function declared in a library module must have
a namespace URI that is the same as the target namespace of the
module; otherwise a static error is raised [err:XQST0048]. In the
statically known namespaces of the
library module, the namespace prefix specified in the module
declaration is bound to the module's target namespace.

Any module may import
one or more library modules by means of a module import that specifies the
target namespace of the library modules to be imported. When a
module imports one or more library modules, the variables and
functions declared in the imported modules are added to the
static
context and (where applicable) to the dynamic context of
the importing module.

The following is an example of a module declaration:

module namespace math = "http://example.org/math-functions";

4.3 Boundary-space Declaration

[11]

BoundarySpaceDecl

::=

"declare" "boundary-space" ("preserve" |
"strip")

[Definition: A boundary-space
declaration sets the boundary-space policy in the
static
context, overriding any implementation-defined default.
Boundary-space policy controls whether boundary
whitespace is preserved by element constructors during
processing of the query.] If boundary-space policy is
preserve, boundary whitespace is preserved. If
boundary-space policy is strip, boundary whitespace is
stripped (deleted). A further discussion of whitespace in
constructed elements can be found in 3.7.1.4 Boundary Whitespace.

4.4 Default Collation
Declaration

[Definition: A default collation
declaration sets the value of the default collation in the static context,
overriding any implementation-defined default.] The default
collation is the collation that is used by functions and operators
that require a collation if no other collation is specified. For
example, the gt operator on strings is defined by a
call to the fn:compare function, which takes an
optional collation parameter. Since the gt operator
does not specify a collation, the fn:compare function
implements gt by using the default collation.

If neither the implementation nor the Prolog specifies a default
collation, the Unicode codepoint collation
(http://www.w3.org/2005/xpath-functions/collation/codepoint)
is used.

The following example illustrates a default collation
declaration:

declare default collation
"http://example.org/languages/Icelandic";

If a default collation declaration specifies a collation by a
relative URI, that relative URI is resolved to an absolute URI
using the base URI in
the static
context. If a Prolog contains more than one default collation
declaration, or the value specified by a default collation
declaration (after resolution of a relative URI, if necessary) is
not present in statically known collations, a
static error is
raised [err:XQST0038].

4.5 Base
URI Declaration

[Definition: A base URI declaration
specifies the base URI
property of the static context. The base URI property is used when resolving
relative URIs within a module.] For example, the fn:doc
function resolves a relative URI using the base URI of the calling
module.

In the terminology of [RFC3986] Section
5.1, the URILiteral of the base URI declaration is considered to be
a "base URI embedded in content". If no base URI declaration is
present, the base URI
in the static
context is established according to the principles outlined in
[RFC3986] Section 5.1—that is, it defaults
first to the base URI of the encapsulating entity, then to the URI
used to retrieve the entity, and finally to an
implementation-defined default. If the URILiteral in the base URI
declaration is a relative URI, then it is made absolute by
resolving it with respect to this same hierarchy. For example, if
the URILiteral in the base URI declaration is
../data/, and the query is contained in a file whose
URI is file:///C:/temp/queries/query.xq, then the
base URI in the
static
context is file:///C:/temp/data/.

It is not intrinsically an error if this process fails to
establish an absolute base URI; however, the base URI in the static context is then undefined [err:XPST0001]. When the base
URI in the static context is undefined, any attempt to use its value to
resolve a relative URI reference will result in an error [err:XPST0001]. When the base
URI of a constructed node is taken from the base URI in the static
context and the latter is undefined, then the base-uri property of the
constructed node is empty.

4.6 Construction Declaration

[30]

ConstructionDecl

::=

"declare" "construction" ("strip" |
"preserve")

[Definition: A construction
declaration sets the construction mode in the static context,
overriding any implementation-defined default.] The construction
mode governs the behavior of element and document node
constructors. If construction mode is preserve, the
type of a constructed element node is xs:anyType, and
all attribute and element nodes copied during node construction
retain their original types. If construction mode is
strip, the type of a constructed element node is
xs:untyped; all element nodes copied during node
construction receive the type xs:untyped, and all
attribute nodes copied during node construction receive the type
xs:untypedAtomic.

4.7 Ordering Mode Declaration

[14]

OrderingModeDecl

::=

"declare" "ordering" ("ordered" |
"unordered")

[Definition: An ordering mode
declaration sets the ordering mode in the static context,
overriding any implementation-defined default.] This ordering mode
applies to all expressions in a module (including both the Prolog and the Query Body, if any), unless overridden by an
ordered or unordered expression.

Ordering
mode affects the behavior of path expressions that include a
"/" or "//" operator or an axis step; union,
intersect, and except expressions; and
FLWOR expressions that have no order by clause. If
ordering mode is ordered, node sequences returned by
path, union, intersect, and
except expressions are in document order; otherwise the order
of these return sequences is implementation-dependent.
The effect of ordering mode on FLWOR expressions is described in
3.8 FLWOR
Expressions.

4.8
Empty Order Declaration

[15]

EmptyOrderDecl

::=

"declare" "default" "order" "empty" ("greatest" |
"least")

[Definition: An empty order
declaration sets the default order for empty sequences in
the static
context, overriding any implementation-defined default. This
declaration controls the processing of empty sequences and
NaN values as ordering keys in an order
by clause in a FLWOR expression.] An individual order
by clause may override the default order for empty sequences
by specifying empty greatest or empty
least.

4.9 Copy-Namespaces Declaration

[Definition: A copy-namespaces
declaration sets the value of copy-namespaces mode in the
static
context, overriding any implementation-defined default.
Copy-namespaces mode controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor or document constructor.] Handling of namespace
bindings by element constructors is described in 3.7.1 Direct Element
Constructors.

4.11
Schema Import

[Definition: A schema import imports
the element declarations, attribute declarations, and type
definitions from a schema into the in-scope schema
definitions. For each user-defined atomic type in the
schema, schema import also adds a corresponding constructor
function. ] The schema to be imported is identified by
its target
namespace. The schema import may bind a namespace prefix to the
target namespace of the imported schema, or may declare that target
namespace to be the default element/type namespace. The
schema import may also provide optional hints for locating the
schema.

The first URILiteral in a
schema import specifies the target namespace of the schema to be
imported. The URILiterals that follow the at keyword
are optional location hints, and can be interpreted or disregarded
in an implementation-dependent way. Multiple location hints might
be used to indicate more than one possible place to look for the
schema or multiple physical resources to be assembled to form the
schema.

A schema import that specifies a zero-length string as target
namespace is considered to import a schema that has no target
namespace. Such a schema import must not bind a namespace prefix
[err:XQST0057], but
it may set the default element/type namespace to a zero-length
string (representing "no namespace"), thus enabling the definitions
in the imported namespace to be referenced. If the default
element/type namespace is not set to "no namespace", there is no
way to reference the definitions in an imported schema that has no
target namespace.

It is a static
error [err:XQST0058] if more than one schema import in
the same Prolog specifies
the same target namespace. It is a static error [err:XQST0059] if the implementation is not able
to process a schema import by finding a valid schema with the
specified target namespace. It is a static error [err:XQST0035] if multiple imported schemas, or
multiple physical resources within one schema, contain definitions
for the same name in the same symbol space (for example, two
definitions for the same element name, even if the definitions are
consistent). However, it is not an error to import the schema with
target namespace http://www.w3.org/2001/XMLSchema
(predeclared prefix xs), even though the built-in
types defined in this schema are implicitly included in the
in-scope schema
types.

It is a static
error [err:XQST0012] if the set of definitions
contained in all schemas imported by a Prolog do not satisfy the
conditions for schema validity specified in Sections 3 and 5 of
[XML Schema] Part 1--i.e., each definition
must be valid, complete, and unique.

The following example imports a schema, specifying both its
target namespace and its location, and binding the prefix
soap to the target namespace:

The following example imports a schema by specifying only its
target namespace, and makes it the default element/type
namespace:

import schema default element namespace "http://example.org/abc";

The following example imports a schema that has no target
namespace, providing a location hint, and sets the default
element/type namespace to "no namespace" so that the definitions in
the imported schema can be referenced:

The following example imports a schema that has no target
namespace and sets the default element/type namespace to "no
namespace". Since no location hint is provided, it is up to the
implementation to find the schema to be imported.

The first URILiteral in a
module import must be of nonzero length [err:XQST0088], and specifies the target
namespace of the modules to be imported. The URILiterals that
follow the at keyword are optional location hints, and
can be interpreted or disregarded in an implementation-defined way.

It is a static
error [err:XQST0047] if more than one module import in
a Prolog specifies the same
target namespace. It is a static error [err:XQST0059] if the implementation is not able
to process a module import by finding a valid module definition
with the specified target namespace. It is a static error if the
expanded
QName and arity of a function declared in an imported module
are respectively equal to the expanded QName and arity of a function
declared in the importing module or in another imported module
(even if the declarations are consistent) [err:XQST0034]. It is a static error if the
expanded
QName of a variable declared in an imported module is equal (as
defined by the eq operator) to the expanded QName of a
variable declared in the importing module or in another imported
module (even if the declarations are consistent) [err:XQST0049].

Each module has its own
static
context. A module import imports only functions and
variable declarations; it does not import other objects from the
imported modules, such as in-scope schema definitions or statically known namespaces. Module
imports are not transitive—that is, importing a module provides
access only to function and variable declarations contained
directly in the imported module. For example, if module A imports
module B, and module B imports module C, module A does not have
access to the functions and variables declared in module C.

A module may import its own target namespace (this is
interpreted as importing an implementation-defined set of
other modules that share its target namespace.)

schema-attribute(AN) appears in the declared type
of a variable in the imported module, and that variable is
referenced in the importing module, OR

schema-attribute(AN) appears in a parameter-type or
result-type of a function declared in the imported module, and that
function is referenced in the importing module.

To illustrate the above rules, suppose that a certain schema
defines a type named triangle. Suppose that a library
module imports the schema, binds its target namespace to the prefix
geometry, and declares a function with the following
function signature: math:area($t
as geometry:triangle) as xs:double. If a query wishes to use
this function, it must import both the library module and
the schema on which it is based. Importing the library module alone
would not provide access to the definition of the type
geometry:triangle used in the signature of the
area function.

If the URILiteral part of a namespace declaration is a
zero-length string, any existing namespace binding for the given
prefix is removed from the statically known namespaces. This
feature provides a way to remove predeclared namespace prefixes
such as local.

In the query result, the newly created node is in the namespace
associated with the namespace URI
http://example.org.

The namespace prefix specified in a namespace declaration must
not be xml or xmlns [err:XQST0070]. The namespace
URI specified in a namespace declaration must not be
http://www.w3.org/XML/1998/namespace or
http://www.w3.org/2000/xmlns/ [err:XQST0070]. The namespace prefix
specified in a namespace declaration must not be the same as any
namespace prefix bound in the same module by a module import,
schema
import, module declaration, or another namespace
declaration [err:XQST0033].

XQuery has several predeclared namespace prefixes that are
present in the statically known namespaces before each
query is processed. These prefixes may be used without an explicit
declaration. They may be overridden by namespace
declarations in a Prolog or by namespace declaration attributes on
constructed elements (however, the prefix xml must not
be redeclared, and no other prefix may be bound to the namespace
URI associated with the prefix xml [err:XQST0070]). The
predeclared namespace prefixes are as follows:

When element or attribute names are compared, they are
considered identical if the local parts and namespace URIs match on
a codepoint basis. Namespace prefixes need not be identical for two
names to match, as illustrated by the following example:

Although the namespace prefixes xx and
foo differ, both are bound to the namespace URI
"http://example.org". Since xx:bing and
foo:bing have the same local name and the same
namespace URI, they match. The output of the above query is as
follows.

4.14 Default Namespace Declaration

Default namespace declarations can be used in a Prolog to facilitate the use of
unprefixed QNames. The following kinds of default namespace
declarations are supported:

A default element/type namespace declaration declares a
namespace URI that is associated with unprefixed names of elements
and types. This declaration is recorded as the default
element/type namespace in the static context. A Prolog may contain at most one default
element/type namespace declaration [err:XQST0066]. If the URILiteral in a default element/type
namespace declaration is a zero-length string, the default
element/type namespace is undeclared (set to "none"), and
unprefixed names of elements and types are considered to be in no
namespace. The following example illustrates the declaration of a
default namespace for elements and types:

If no default element/type namespace declaration is present,
unprefixed element and type names are in no namespace (however, an
implementation may define a different default as specified in
C.1 Static Context
Components.)

A default function namespace declaration declares a
namespace URI that is associated with unprefixed function names in
function calls and function declarations. This declaration is
recorded as the default function namespace in the static context. A
Prolog may contain at most
one default function namespace declaration [err:XQST0066]. If the StringLiteral in a
default function namespace declaration is a zero-length string, the
default function namespace is undeclared (set to "none"). In that
case, any functions that are associated with a namespace can be
called only by using an explicit namespace prefix.

If no default function namespace declaration is present, the
default function namespace is the namespace of XPath/XQuery
functions, http://www.w3.org/2005/xpath-functions
(however, an implementation may define a different default as
specified in C.1
Static Context Components.)

The following example illustrates the declaration of a default
function namespace:

The effect of declaring a default function namespace is that all
functions in the default function namespace, including
implicitly-declared constructor functions, can be
invoked without specifying a namespace prefix. When a function call
uses a function name with no prefix, the local name of the function
must match a function (including implicitly-declared constructor
functions) in the default function namespace [err:XPST0017].

A variable declaration always refers to a declaration of
a variable in a Prolog. The binding of a variable to a value in a
query expression, such as a FLWOR expression, is known as a
variable binding, and does not make the variable visible to
an importing module.

During static analysis, a variable declaration causes a pair
(expanded QName N, type T) to be added to the
in-scope variables. The expanded QName
N is the VarName. If N is equal (as defined by the eq
operator) to the expanded QName of another variable in in-scope
variables, a static
error is raised [err:XQST0049].

All variable names declared in a library module must (when
expanded) be in the target namespace of the library module
[err:XQST0048].
When a library module is imported, variables declared in the
imported module are added to the in-scope variables of the
importing module.

Variable names that have no namespace prefix are in no
namespace. Variable declarations that have no namespace prefix may
appear only in a main module.

The type T is as follows:

If TypeDeclaration is present, then the
SequenceType in the TypeDeclaration;
otherwise

If the Static Typing Feature is in effect and
VarValue is present, then the static type inferred
from static analysis of the expression VarValue;

Note:

Type inference might not be computable until after the check for
circular dependencies, described below, is complete.

Otherwise, item()*.

[Definition: If a variable
declaration includes an expression (VarValue or
VarDefaultValue), the expression is called an
initializing expression. The static context for an
initializing expression includes all functions, variables, and
namespaces that are declared or imported anywhere in the Prolog,
other than the variable being declared.]

[Definition: An expression
Edepends on a variableV if any
of the following is true:

During query evaluation, each variable declaration causes a pair
(expanded QName N, value V) to be added to the
Prologvariable values.
The expanded QName N is the VarName. The value V is as
follows:

If VarValue is specified, then V is the result of
evaluating VarValue as described below.

If external is specified, then:

if a value is provided for the variable by the external
environment, then V is that value. The means by which typed values
of external variables are provided by the external environment is
implementation-defined.

if no value is provided for the variable by the external
environment, and VarDefaultValue is specified, then V
is the result of evaluating VarDefaultValue as
described below.

If no value is provided for the variable by the external
environment, and VarDefaultValue is not specified,
then a dynamic
error is raised [err:XPDY0002].

It is implementation-dependent whether this error is raised if
the evaluation of the query does not reference the value of the
variable.

In all cases the value V must match the type T according to the
rules for SequenceType matching; otherwise a type error is raised [err:XPTY0004].

If VarValue or VarDefaultValue is
evaluated, the dynamic context for the evaluation is as
follows:

The variable values contain the values of all
variables present in the static context.

Note:

A cyclic dependency between variables is a static error, so it
is always possible to evaluate all the variables that V depends on
before evaluating V.)

The function implementations contains the implementation of each
function present in the static context

All other properties of the dynamic context, including the
context item, position, and size, are the same as for the
evaluation of the QueryBody of the main module.

Here are some examples of variable declarations:

The following declaration specifies both the type and the value
of a variable. This declaration causes the type
xs:integer to be associated with variable
$x in the static context, and the value
7 to be associated with variable $x in
the dynamic
context.

declare variable $x as xs:integer := 7;

The following declaration specifies a value but not a type. The
static type of
the variable is inferred from the static type of its value. In this
case, the variable $x has a static type of
xs:decimal, inferred from its value which is 7.5.

declare variable $x := 7.5;

The following declaration specifies a type but not a value. The
keyword external indicates that the value of the
variable will be provided by the external environment. At
evaluation time, if the variable $x in the dynamic context
does not have a value of type xs:integer, a type error is raised.

declare variable $x as xs:integer external;

The following declaration specifies neither a type nor a value.
It simply declares that the query depends on the existence of a
variable named $x, whose type and value will be
provided by the external environment. During query analysis, the
type of $x is considered to be item()*.
During query evaluation, the dynamic context must include a type and a
value for $x, and its value must be compatible with
its type.

declare variable $x external;

The following declaration, which might appear in a library
module, declares a variable whose name includes a namespace
prefix:

declare variable $math:pi as xs:double := 3.14159E0;

This is an example of an external variable declaration that
provides a VarDefaultValue:

4.16 Context Item
Declaration

A context item declaration allows a query to specify the
static type,
value, or default value for the initial context item.

When a context item declaration appears in a library module,
neither VarValue nor VarDefaultValue may
be specified. Such a context item declaration serves only to
declare the expected type of the context item.

In every module that does not contain a context item
declaration, the effect is as if the declaration

declare context item as item() external;

appeared in that module.

During static analysis, the context item declaration has the
effect of setting the context item static type in the static
context. The context item static type is set to
ItemType if specified, or to item()
otherwise.

If a module contains more than one context item declaration, a
static error is raised [err:XQST0099].

The static context for an initializing expression includes all
functions, variables, and namespaces that are declared or imported
anywhere in the Prolog.

[Definition: An expression
Edepends on the context item if any of the
following is true:

E is "."

E is position() or
last()

E is an axis step

E is a call to a built-in function that takes the
context item as an implicit argument

E has a subexpression that depends on the context
item, and E does not bind the context item for that
subexpression

During query evaluation, the context item in the dynamic context
for the evaluation of the QueryBody in the main
module, and for the initializing expression of every variable
declaration in every module, is set as follows:

If VarValue is specified, then the result of
evaluating VarValue as described below.

If external is specified, then:

if a value is provided for the context item by the external
environment, then that value.

The means by which an external value is provided by the external
environment is implementation-defined.

if no value is provided for the context item by the external
environment, and VarDefaultValue is specified, then
the result of evaluating VarDefaultValue as described
below.

if no value is provided for the context item by the external
environment, and VarDefaultValue is not specified,
then the context item is undefined, and a dynamic error is raised
[err:XPDY0002] if
the context item is referenced in the query.

In all cases where the context item has a value, that value must
match the type T according to the rules for
SequenceType matching; otherwise a type error is raised [err:XPTY0004]. If more than
one module contains a context item declaration, the context item
must match the type declared in each one.

If VarValue or VarDefaultValue is
evaluated, the dynamic context for the evaluation is as
follows:

The variable values contains the values of all variables present
in the static context

4.17 Function
Declaration

In addition to the built-in functions described in [XQuery and XPath Functions and Operators
1.1], XQuery allows users to declare functions of their own. A
function declaration specifies the name of the function, the names
and datatypes of the parameters, and the datatype of the result.
All datatypes are specified using the syntax described in 2.5 Types. A function declaration causes the
declared function to be added to the function signatures of the
module in which it
appears.

[Definition: User defined functions are
functions that contain a function body, which provides the
implementation of the function as an XQuery expression.] The
static
context for a function body includes all functions, variables,
and namespaces that are declared or imported anywhere in the
Prolog, including the
function being declared.

[Definition: External functions
are functions that are implemented outside the query environment.]
For example, an XQuery implementation might provide a set of
external functions in addition to the core function library
described in [XQuery and XPath
Functions and Operators 1.1]. External functions are identified
by the keyword external. The purpose of a function
declaration for an external function is to declare the datatypes of
the function parameters and result, for use in type checking of the
query that contains or imports the function declaration.

A function declaration may specify that an external function is
deterministic (which is the default) or nondeterministic.
[Definition: A deterministic
function is a function that always evaluates to the same result
if it is invoked with the same arguments.] [Definition: A
nondeterministic function is a function that is not
guaranteed to always return the same result when it is invoked with
the same arguments.]. An XQuery processor can use static analysis
to determine whether a user-defined function is deterministic (the
syntax of function declarations does not allow a user-defined
function to be declared deterministic or nondeterministic).

When rewriting expressions into equivalent expressions, as
described in 2.3.4 Errors and
Optimization, a conforming XQuery implementation must
ensure that each run-time invocation of a nondeterministic function
in the original expression results in exactly one run-time
invocation of the function in the rewritten expression. For
instance, suppose the random() function is declared to
be nondeterministic:

An XQuery implementation may provide a facility whereby external
functions can be implemented using a host programming language, but
it is not required to do so. If such a facility is provided, the
protocols by which parameters are passed to an external function,
and the result of the function is returned to the invoking query,
are implementation-defined. An XQuery
implementation may augment the type system of [XQuery and XPath Data Model (XDM) 1.1]
with additional types that are designed to facilitate exchange of
data with host programming languages, or it may provide mechanisms
for the user to define such types. For example, a type might be
provided that encapsulates an object returned by an external
function, such as an SQL database connection. These additional
types, if defined, are considered to be derived by restriction from
xs:anyAtomicType.

Every user-defined function must be in a namespace--that is,
every declared function name must (when expanded) have a non-null
namespace URI [err:XQST0060]. If the function name in a
function declaration has no namespace prefix, it is considered to
be in the default function namespace. Every function name
declared in a library module must (when expanded) be in
the target
namespace of the library module [err:XQST0048]. It is a static error [err:XQST0045] if the function name in a
function declaration (when expanded) is in any of the following
namespaces:

In order to allow main modules to declare functions for local
use within the module without defining a new namespace, XQuery
predefines the namespace prefix local to the namespace
http://www.w3.org/2005/xquery-local-functions. It is
suggested (but not required) that this namespace be used for
defining local functions.

If a function parameter is declared using a name but no type,
its default type is item()*. If the result type is
omitted from a function declaration, its default result type is
item()*.

The parameters of a function declaration are considered to be
variables whose scope is the function body. It is an static error [err:XQST0039] for a function
declaration to have more than one parameter with the same name. The
type of a function parameter can be any type that can be expressed
as a sequence
type.

The following example illustrates the declaration and use of a
local function that accepts a sequence of employee
elements, summarizes them by department, and returns a sequence of
dept elements.

Using a function, prepare a summary of employees that are
located in Denver.

Rules for converting function arguments to their declared
parameter types, and for converting the result of a function to its
declared result type, are described in 3.1.5 Function Calls.

A function declaration may be recursive—that is, it may
reference itself. Mutually recursive functions, whose bodies
reference each other, are also allowed. The following example
declares a recursive function that computes the maximum depth of a
node hierarchy, and calls the function to find the maximum depth of
a particular document. In its declaration, the user-declared
function local:depth calls the built-in functions
empty and max, which are in the default
function namespace.

Find the maximum depth of the document named
partlist.xml.

declare function local:depth($e as node()) as xs:integer
{
(: A node with no children has depth 1 :)
(: Otherwise, add 1 to max depth of children :)
if (fn:empty($e/*)) then 1
else fn:max(for $c in $e/* return local:depth($c)) + 1
};
local:depth(fn:doc("partlist.xml"))

Each implementation recognizes an implementation-defined set of
namespace URIs used to denote option declarations.

If the namespace part of the QName is not a namespace recognized
by the implementation as one used to denote option declarations,
then the option declaration is ignored.

Otherwise, the effect of the option declaration, including its
error behavior, is implementation-defined. For
example, if the local part of the QName is not recognized, or if
the StringLiteral does not conform to the rules defined by the
implementation for the particular option declaration, the
implementation may choose whether to report an error, ignore the
option declaration, or take some other action.

Implementations may impose rules on where particular option
declarations may appear relative to variable declarations and
function declarations, and the interpretation of an option
declaration may depend on its position.

An option declaration must not be used to change the syntax
accepted by the processor, or to suppress the detection of
static errors.
However, it may be used without restriction to modify the semantics
of the query. The scope of the option declaration is implementation-defined—for
example, an option declaration might apply to the whole query, to
the current module, or to the immediately following function
declaration.

The following examples illustrate several possible uses for
option declarations:

This option declaration might be used to specify how comments in
source documents returned by the fn:doc() function
should be handled:

declare option exq:strip-comments "true";

This option declaration might be used to associate a namespace
used in function names with a Java class:

5 Conformance

Note:

The XQuery Working Group has not yet determined conformance
criteria for XQuery 1.1; in particular, we have not decided which
of the new features of XQuery 1.1 are optional. This section
currently contains the conformance criteria for XQuery 1.0, with
two modifications: (1) support for all axes is now required, (2)
conformance criteria for syntax extensions are given.

This section defines the conformance criteria for an XQuery
processor. In this section, the following terms are used to
indicate the requirement levels defined in [RFC
2119]. [Definition:
MUST means that the item is an absolute requirement of the
specification.] [Definition:
MAY means that an item is truly optional.] [Definition: SHOULD
means that there may exist valid reasons in particular
circumstances to ignore a particular item, but the full
implications must be understood and carefully weighed before
choosing a different course.]

An XQuery processor that claims to conform to this specification
MUST include a claim of Minimal
Conformance as defined in 5.1
Minimal Conformance. In addition to a claim of Minimal
Conformance, it MAY claim
conformance to one or more optional features defined in 5.2 Optional
Features.

5.1 Minimal Conformance

Minimal Conformance to this specification MUST include all of the following items:

Support for everything specified in this document except those
features specified in 5.2 Optional Features to
be optional. If an implementation does not provide a given optional
feature, it MUST implement any
requirements specified in 5.2 Optional Features
for implementations that do not provide that feature.

5.2.3 Static Typing Feature

If an implementation supports the Static
Typing Feature, then it MUST
report an error during static analysis whenever the inferred static
type of an expression is not subsumed by the required type for the
context in which it appears.

If an implementation does not support the Static
Typing Feature, then it MAY
report type errors during the static analysis phase only in cases
where the inferred static type and the required type have an empty
intersection (that is, where evaluation of the expression is
guaranteed to fail). It MAY defer
some or all type checking until the dynamic evaluation phase.

5.2.4
Module Feature

[Definition: A conforming XQuery
implementation that supports the Module Feature allows a
query Prolog to contain a Module Import and allows
library modules to be created.]

Not all implementations need to serialize. For instance, an
implementation might provide results via an XML API instead of
producing a textual representation.

5.3 Data Model Conformance

All XQuery implementations process data represented in the
data model as
specified in [XQuery and XPath Data
Model (XDM) 1.1]. The data model specification relies on
languages such as XQuery to specify conformance criteria for the
data model in their respective environments, and suggests that the
following issues should be considered:

Support for normative construction from an infoset. A
conforming implementation MAY choose
to claim conformance to Section 3.2
Construction from an InfosetDM, which
defines a normative way to construct an XDM instance from an XML
document that is merely well-formed or is governed by a DTD.

Support for normative construction from a PSVI. A
conforming implementation MAY choose
to claim conformance to Section 3.3
Construction from a PSVIDM, which
defines a normative way to construct an XDM instance from an XML
document that is governed by a W3C XML Schema.

At the time of writing there is no published version of XML
Schema that references the XML 1.1 specifications. This means that
datatypes such as xs:NCName and xs:ID are
constrained by the XML 1.0 rules. It is recommended that an XQuery
1.0 processor should implement the rules defined by later versions
of XML Schema as they become available.

For the xs:decimal type, the maximum number of
decimal digits (totalDigits facet) (must be at least
18).

For the types xs:date, xs:time,
xs:dateTime, xs:gYear, and
xs:gYearMonth: the maximum value of the year component
and the maximum number of fractional second digits (must be at
least 3).

For the xs:duration type: the maximum absolute
values of the years, months, days, hours, minutes, and seconds
components.

For the xs:yearMonthDuration type: the maximum
absolute value, expressed as an integer number of months.

For the xs:dayTimeDuration type: the maximum
absolute value, expressed as a decimal number of seconds.

For the types xs:string, xs:hexBinary,
xs:base64Binary, xs:QName,
xs:anyURI, xs:NOTATION, and types derived
from them: limitations (if any) imposed by the implementation on
lengths of values.

The limits listed above need not be fixed, but may depend on
environmental factors such as system resources. For example, the
length of a value of type xs:string may be limited by
available memory.

5.4 Syntax Extensions

Any syntactic extensions to XQuery are implementation-defined. The effect
of syntactic extensions, including their error behavior, is
implementation-defined. Syntactic
extensions may be used without restriction to modify the semantics
of a XQuery expression.

A XQuery 1.1 Grammar

A.1 EBNF

The grammar of XQuery 1.1 uses the same simple Extended
Backus-Naur Form (EBNF) notation as [XML 1.0]
with the following minor differences.

All named symbols have a name that begins with an uppercase
letter.

It adds a notation for referring to productions in external
specs.

Comments or extra-grammatical constraints on grammar productions
are between '/*' and '*/' symbols.

A.1.1
Notation

The following definitions will be helpful in defining precisely
this exposition.

[Definition:
Each rule in the grammar defines one symbol, using the
following format:

symbol ::= expression

]

[Definition: A terminal is a symbol or string
or pattern that can appear in the right-hand side of a rule, but
never appears on the left hand side in the main grammar, although
it may appear on the left-hand side of a rule in the grammar for
terminals.] The following constructs are used to match strings of
one or more characters in a terminal:

matches any Char with a value
among the characters enumerated. Enumerations and ranges can
be mixed in one set of brackets.

[^abc]

matches any Char with a value
not among the characters given. Enumerations and ranges of
forbidden values can be mixed in one set of brackets.

"string"

matches the sequence of characters that appear inside the double
quotes.

'string'

matches the sequence of characters that appear inside the single
quotes.

[http://www.w3.org/TR/REC-example/#NT-Example]

matches any string matched by the production defined in the
external specification as per the provided reference.

Patterns (including the above constructs) can be combined with
grammatical operators to form more complex patterns, matching more
complex sets of character strings. In the examples that follow, A
and B represent (sub-)patterns.

(A)

A is treated as a unit and may be combined as
described in this list.

A?

matches A or nothing; optional A.

A B

matches A followed by B. This operator
has higher precedence than alternation; thus A B | C D
is identical to (A B) | (C D).

A | B

matches A or B but not both.

A - B

matches any string that matches A but does not
match B.

A+

matches one or more occurrences of A. Concatenation
has higher precedence than alternation; thus A+ | B+
is identical to (A+) | (B+).

A*

matches zero or more occurrences of A.
Concatenation has higher precedence than alternation; thus A*
| B* is identical to (A*) | (B*)

A.1.2 Extra-grammatical
Constraints

This section contains constraints on the EBNF productions, which
are required to parse legal sentences. The notes below are
referenced from the right side of the production, with the
notation: /* xgc: <id> */.

Constraint:
leading-lone-slash

A single slash may appear either as a complete path expression
or as the first part of a path expression in which it is followed
by a RelativePathExpr.
In some cases, the next token after the slash is insufficient to
allow a parser to distinguish these two possibilities: the
* token and keywords like union could be
either an operator or a NameTest, and
the < token could be either an operator or the
start of a DirectConstructor .
For example, without lookahead the first part of the expression
/ * 5 is easily taken to be a complete expression,
/ *, which has a very different interpretation (the
child nodes of /).

Therefore to reduce the need for lookahead, if the token
immediately following a slash can form the start of a RelativePathExpr, then the
slash must be the beginning of a PathExpr, not the entirety of it.

A single slash may be used as the left-hand argument of an
operator by parenthesizing it: (/) * 5. The expression
5 * /, on the other hand, is legal without
parentheses.

Constraint: xml-version

An implementation's choice to support the [XML
1.0] and [XML Names], or [XML 1.1] and [XML Names
1.1] lexical specification determines the external document
from which to obtain the definition for this production. The EBNF
only has references to the 1.0 versions. In some cases, the XML 1.0
and XML 1.1 definitions may be exactly the same. Also please note
that these external productions follow the whitespace rules of
their respective specifications, and not the rules of this
specification, in particular A.2.4.1 Default Whitespace
Handling. Thus prefix : localname is not a
valid QName for purposes of this specification, just as it is not
permitted in a XML document. Also, comments are not permissible on
either side of the colon. Also extra-grammatical constraints such
as well-formedness constraints must be taken into account.

Constraint:
reserved-function-names

Unprefixed function names spelled the same way as language
keywords could make the language harder to recognize. For instance,
if(foo) could be taken either as a FunctionCall or as the beginning
of an IfExpr. Therefore it is
not legal syntax for a user to invoke functions with unprefixed
names which match any of the names in A.3 Reserved Function Names.

A function named "if" can be called by binding its namespace to
a prefix and using the prefixed form: "library:if(foo)" instead of
"if(foo)".

Constraint:
occurrence-indicators

As written, the grammar in A XQuery 1.1
Grammar is ambiguous for some forms using the '+' and '*'
Kleene operators. The ambiguity is resolved as follows: these
operators are tightly bound to the SequenceType expression, and have
higher precedence than other uses of these symbols. Any occurrence
of '+' and '*', as well as '?', following a sequence type is
assumed to be an occurrence indicator. That is, a "+", "*", or "?"
immediately following an ItemType must be an OccurrenceIndicator. Thus,
4 treat as item() + - 5 must be interpreted as
(4 treat as item()+) - 5, taking the '+' as an
OccurrenceIndicator and the '-' as a subtraction operator. To force
the interpretation of "+" as an addition operator (and the
corresponding interpretation of the "-" as a unary minus),
parentheses may be used: the form (4 treat as item()) +
-5 surrounds the SequenceType expression with
parentheses and leads to the desired interpretation.

This rule has as a consequence that certain forms which would
otherwise be legal and unambiguous are not recognized: in "4 treat
as item() + 5", the "+" is taken as an OccurrenceIndicator, and
not as an operator, which means this is not a legal expression.

A.1.3
Grammar Notes

This section contains general notes on the EBNF productions,
which may be helpful in understanding how to interpret and
implement the EBNF. These notes are not normative. The notes below
are referenced from the right side of the production, with the
notation: /* gn: <id> */.

Note:

grammar-note: parens

Look-ahead is required to distinguish FunctionCall from a QName or
keyword followed by a Pragma orComment. For example: address (:
this may be empty :) may be mistaken for a call to a
function named "address" unless this lookahead is employed. Another
example is for (: whom the bell :) $tolls in 3 return
$tolls, where the keyword "for" must not be mistaken for a
function name.

A comment can contain nested comments, as long as all "(:" and
":)" patterns are balanced, no matter where they occur within the
outer comment.

Note:

Lexical analysis may typically handle nested comments by
incrementing a counter for each "(:" pattern, and decrementing the
counter for each ":)" pattern. The comment does not terminate until
the counter is back to zero.

Some illustrative examples:

(: commenting out a (: comment :) may be confusing, but
often helpful :) is a legal Comment, since balanced nesting
of comments is allowed.

"this is just a string :)" is a legal expression.
However, (: "this is just a string :)" :) will cause a
syntax error. Likewise, "this is another string (:" is
a legal expression, but (: "this is another string (:"
:) will cause a syntax error. It is a limitation of nested
comments that literal content can cause unbalanced nesting of
comments.

for (: set up loop :) $i in $x return $i is
syntactically legal, ignoring the comment.

5 instance (: strange place for a comment :) of
xs:integer is also syntactically legal.

<eg (: an example:)>{$i//title}</eg> is
not syntactically legal.

<eg> (: an example:) </eg> is
syntactically legal, but the characters that look like a comment
are in fact literal element content.

A.2
Lexical structure

The terminal symbols assumed by the grammar above are described
in this section.

It is customary to separate consecutive terminal symbols by
whitespace and
Comments, but this is required
only when otherwise two non-delimiting symbols would be adjacent to
each other. There are two exceptions to this, that of "." and "-",
which do require a symbol separator if they follow a QName or
NCName. Also, "." requires a separator if it precedes or follows a
numeric literal.

A.2.3
End-of-Line Handling

The XQuery 1.1 processor must behave as if it normalized all
line breaks on input, before parsing. The normalization should be
done according to the choice to support either [XML
1.0] or [XML 1.1] lexical processing.

A.2.3.1 XML 1.0 End-of-Line
Handling

For [XML 1.0] processing, all of the
following must be translated to a single #xA character:

the two-character sequence #xD #xA

any #xD character that is not immediately followed by #xA.

A.2.3.2 XML 1.1 End-of-Line
Handling

For [XML 1.1] processing, all of the
following must be translated to a single #xA character:

the two-character sequence #xD #xA

the two-character sequence #xD #x85

the single character #x85

the single character #x2028

any #xD character that is not immediately followed by #xA or
#x85.

The characters #x85 and #x2028 cannot be reliably
recognized and translated until the VersionDecl declaration (if
present) has been read.

A.2.4
Whitespace Rules

A.2.4.1 Default Whitespace
Handling

[Definition: Ignorable whitespace
consists of any whitespace characters that may occur between
terminals, unless these
characters occur in the context of a production marked with a
ws:explicit annotation,
in which case they can occur only where explicitly specified (see
A.2.4.2 Explicit
Whitespace Handling).] Ignorable whitespace characters are
not significant to the semantics of an expression. Whitespace is
allowed before the first terminal and after the last terminal of a
module. Whitespace is allowed between any two terminals. Comments may also act as "whitespace"
to prevent two adjacent terminals from being recognized as one.
Some illustrative examples are as follows:

foo- foo results in a syntax error. "foo-" would be
recognized as a QName.

foo -foo is syntactically equivalent to foo -
foo, two QNames separated by a subtraction operator.

foo(: This is a comment :)- foo is syntactically
equivalent to foo - foo. This is because the comment
prevents the two adjacent terminals from being recognized as
one.

foo-foo is syntactically equivalent to single
QName. This is because "-" is a valid character in a QName. When
used as an operator after the characters of a name, the "-" must be
separated from the name, e.g. by using whitespace or
parentheses.

10div 3 results in a syntax error.

10 div3 also results in a syntax error.

10div3 also results in a syntax error.

A.2.4.2 Explicit Whitespace
Handling

Explicit whitespace notation is specified with the EBNF
productions, when it is different from the default rules, using the
notation shown below. This notation is not inherited. In other
words, if an EBNF rule is marked as /* ws: explicit */, the
notation does not automatically apply to all the 'child' EBNF
productions of that rule.

For example,
whitespace is not freely allowed by the direct constructor
productions, but is specified explicitly in the grammar, in order
to be more consistent with XML.

A.3 Reserved Function Names

The following names are not allowed as function names in an
unprefixed form because expression syntax takes precedence.

attribute

comment

document-node

element

empty-sequence

if

item

node

processing-instruction

schema-attribute

schema-element

text

function

typeswitch

A.4
Precedence Order (Non-Normative)

The grammar in A.1 EBNF
normatively defines built-in precedence among the operators of
XQuery. These operators are summarized here to make clear the order
of their precedence from lowest to highest. The associativity
column indicates the order in which operators of equal precedence
in an expression are applied.

In the "Associativity" column, "either" indicates that all the
operators at that level have the associative property (i.e.,
(A op B) op C is equivalent to A op (B op
C)), so their associativity is inconsequential. "NA" (not
applicable) indicates that the EBNF does not allow an expression
that directly contains multiple operators from that precedence
level, so the question of their associativity does not arise.

Note:

Parentheses can be used to override the operator precedence in
the usual way. Square brackets in an expression such as A[B] serve
two roles: they act as an operator causing B to be evaluated once
for each item in the value of A, and they act as parentheses
enclosing the expression B.

Curly braces in an expression such as validate{E}
or ordered{E} perform a similar bracketing role to the parentheses
in a function call, but with the difference in most cases that E is
an Expr rather than ExprSingle, meaning that it can use the comma
operator.

A value of type xs:float (or any type derived by
restriction from xs:float) can be promoted to the type
xs:double. The result is the xs:double
value that is the same as the original value.

A value of type xs:decimal (or any type derived by
restriction from xs:decimal) can be promoted to either
of the types xs:float or xs:double. The
result of this promotion is created by casting the original value
to the required type. This kind of promotion may cause loss of
precision.

URI type promotion: A value of type xs:anyURI (or
any type derived by restriction from xs:anyURI) can be
promoted to the type xs:string. The result of this
promotion is created by casting the original value to the type
xs:string.

Note:

Since xs:anyURI values can be promoted to
xs:string, functions and operators that compare
strings using the default collation also compare
xs:anyURI values using the default collation.
This ensures that orderings that include strings,
xs:anyURI values, or any combination of the two types
are consistent and well-defined.

A function that expects a parameter $p of type
xs:float can be invoked with a value of type
xs:decimal. This is an example of type promotion. The
value is actually converted to the expected type. Within the body
of the function, $p instance of xs:decimal returns
false.

A function that expects a parameter $p of type
xs:decimal can be invoked with a value of type
xs:integer. This is an example of subtype
substitution. The value retains its original type. Within the
body of the function, $p instance of xs:integer
returns true.

B.2 Operator Mapping

The operator mapping tables in this section list the
combinations of types for which the various operators of XQuery 1.1
are defined. [Definition:
For each operator and valid combination of operand types, the
operator mapping tables specify a result type and an operator
function that implements the semantics of the operator for the
given types.] The definitions of the operator functions are given
in [XQuery and XPath Functions and
Operators 1.1]. The result of an operator may be the raising of
an error by its operator function, as defined in [XQuery and XPath Functions and Operators
1.1]. In some cases, the operator function does not implement
the full semantics of a given operator. For the definition of each
operator (including its behavior for empty sequences or sequences
of length greater than one), see the descriptive material in the
main part of this document.

The and and or operators are defined
directly in the main body of this document, and do not occur in the
operator mapping tables.

If an operator in the operator mapping tables expects an operand
of type ET, that operator can be applied to an operand of
type AT if type AT can be converted to type
ET by a combination of type promotion and subtype
substitution. For example, a table entry indicates that the
gt operator may be applied to two xs:date
operands, returning xs:boolean. Therefore, the
gt operator may also be applied to two (possibly
different) subtypes of xs:date, also returning
xs:boolean.

[Definition: When referring to a type, the term
numeric denotes the types xs:integer,
xs:decimal, xs:float, and
xs:double.] An operator whose operands and result are
designated as numeric
might be thought of as representing four operators, one for each of
the numeric types. For example, the numeric + operator
might be thought of as representing the following four
operators:

Operator

First operand type

Second operand type

Result type

+

xs:integer

xs:integer

xs:integer

+

xs:decimal

xs:decimal

xs:decimal

+

xs:float

xs:float

xs:float

+

xs:double

xs:double

xs:double

A numeric operator may be validly applied to an operand of type
AT if type AT can be converted to any of the four
numeric types by a combination of type promotion and subtype
substitution. If the result type of an operator is listed as
numeric, it means "the first type in the ordered list
(xs:integer, xs:decimal, xs:float, xs:double) into
which all operands can be converted by subtype
substitution and type promotion." As an example, suppose
that the type hatsize is derived from
xs:integer and the type shoesize is
derived from xs:float. Then if the +
operator is invoked with operands of type hatsize and
shoesize, it returns a result of type
xs:float. Similarly, if + is invoked with
two operands of type hatsize it returns a result of
type xs:integer.

[Definition: In the operator mapping tables, the
term Gregorian refers to the types
xs:gYearMonth, xs:gYear,
xs:gMonthDay, xs:gDay, and
xs:gMonth.] For binary operators that accept two
Gregorian-type operands, both operands must have the same type (for
example, if one operand is of type xs:gDay, the other
operand must be of type xs:gDay.)

Binary Operators

Operator

Type(A)

Type(B)

Function

Result type

A + B

numeric

numeric

op:numeric-add(A, B)

numeric

A + B

xs:date

xs:yearMonthDuration

op:add-yearMonthDuration-to-date(A, B)

xs:date

A + B

xs:yearMonthDuration

xs:date

op:add-yearMonthDuration-to-date(B, A)

xs:date

A + B

xs:date

xs:dayTimeDuration

op:add-dayTimeDuration-to-date(A, B)

xs:date

A + B

xs:dayTimeDuration

xs:date

op:add-dayTimeDuration-to-date(B, A)

xs:date

A + B

xs:time

xs:dayTimeDuration

op:add-dayTimeDuration-to-time(A, B)

xs:time

A + B

xs:dayTimeDuration

xs:time

op:add-dayTimeDuration-to-time(B, A)

xs:time

A + B

xs:dateTime

xs:yearMonthDuration

op:add-yearMonthDuration-to-dateTime(A, B)

xs:dateTime

A + B

xs:yearMonthDuration

xs:dateTime

op:add-yearMonthDuration-to-dateTime(B, A)

xs:dateTime

A + B

xs:dateTime

xs:dayTimeDuration

op:add-dayTimeDuration-to-dateTime(A, B)

xs:dateTime

A + B

xs:dayTimeDuration

xs:dateTime

op:add-dayTimeDuration-to-dateTime(B, A)

xs:dateTime

A + B

xs:yearMonthDuration

xs:yearMonthDuration

op:add-yearMonthDurations(A, B)

xs:yearMonthDuration

A + B

xs:dayTimeDuration

xs:dayTimeDuration

op:add-dayTimeDurations(A, B)

xs:dayTimeDuration

A - B

numeric

numeric

op:numeric-subtract(A, B)

numeric

A - B

xs:date

xs:date

op:subtract-dates(A, B)

xs:dayTimeDuration

A - B

xs:date

xs:yearMonthDuration

op:subtract-yearMonthDuration-from-date(A, B)

xs:date

A - B

xs:date

xs:dayTimeDuration

op:subtract-dayTimeDuration-from-date(A, B)

xs:date

A - B

xs:time

xs:time

op:subtract-times(A, B)

xs:dayTimeDuration

A - B

xs:time

xs:dayTimeDuration

op:subtract-dayTimeDuration-from-time(A, B)

xs:time

A - B

xs:dateTime

xs:dateTime

op:subtract-dateTimes(A, B)

xs:dayTimeDuration

A - B

xs:dateTime

xs:yearMonthDuration

op:subtract-yearMonthDuration-from-dateTime(A, B)

xs:dateTime

A - B

xs:dateTime

xs:dayTimeDuration

op:subtract-dayTimeDuration-from-dateTime(A, B)

xs:dateTime

A - B

xs:yearMonthDuration

xs:yearMonthDuration

op:subtract-yearMonthDurations(A, B)

xs:yearMonthDuration

A - B

xs:dayTimeDuration

xs:dayTimeDuration

op:subtract-dayTimeDurations(A, B)

xs:dayTimeDuration

A * B

numeric

numeric

op:numeric-multiply(A, B)

numeric

A * B

xs:yearMonthDuration

numeric

op:multiply-yearMonthDuration(A, B)

xs:yearMonthDuration

A * B

numeric

xs:yearMonthDuration

op:multiply-yearMonthDuration(B, A)

xs:yearMonthDuration

A * B

xs:dayTimeDuration

numeric

op:multiply-dayTimeDuration(A, B)

xs:dayTimeDuration

A * B

numeric

xs:dayTimeDuration

op:multiply-dayTimeDuration(B, A)

xs:dayTimeDuration

A idiv B

numeric

numeric

op:numeric-integer-divide(A, B)

xs:integer

A div B

numeric

numeric

op:numeric-divide(A, B)

numeric; but xs:decimal if both operands are xs:integer

A div B

xs:yearMonthDuration

numeric

op:divide-yearMonthDuration(A, B)

xs:yearMonthDuration

A div B

xs:dayTimeDuration

numeric

op:divide-dayTimeDuration(A, B)

xs:dayTimeDuration

A div B

xs:yearMonthDuration

xs:yearMonthDuration

op:divide-yearMonthDuration-by-yearMonthDuration (A, B)

xs:decimal

A div B

xs:dayTimeDuration

xs:dayTimeDuration

op:divide-dayTimeDuration-by-dayTimeDuration (A, B)

xs:decimal

A mod B

numeric

numeric

op:numeric-mod(A, B)

numeric

A eq B

numeric

numeric

op:numeric-equal(A, B)

xs:boolean

A eq B

xs:boolean

xs:boolean

op:boolean-equal(A, B)

xs:boolean

A eq B

xs:string

xs:string

op:numeric-equal(fn:compare(A, B), 0)

xs:boolean

A eq B

xs:date

xs:date

op:date-equal(A, B)

xs:boolean

A eq B

xs:time

xs:time

op:time-equal(A, B)

xs:boolean

A eq B

xs:dateTime

xs:dateTime

op:dateTime-equal(A, B)

xs:boolean

A eq B

xs:duration

xs:duration

op:duration-equal(A, B)

xs:boolean

A eq B

Gregorian

Gregorian

op:gYear-equal(A, B) etc.

xs:boolean

A eq B

xs:hexBinary

xs:hexBinary

op:hexBinary-equal(A, B)

xs:boolean

A eq B

xs:base64Binary

xs:base64Binary

op:base64Binary-equal(A, B)

xs:boolean

A eq B

xs:anyURI

xs:anyURI

op:numeric-equal(fn:compare(A, B), 0)

xs:boolean

A eq B

xs:QName

xs:QName

op:QName-equal(A, B)

xs:boolean

A eq B

xs:NOTATION

xs:NOTATION

op:NOTATION-equal(A, B)

xs:boolean

A ne B

numeric

numeric

fn:not(op:numeric-equal(A, B))

xs:boolean

A ne B

xs:boolean

xs:boolean

fn:not(op:boolean-equal(A, B))

xs:boolean

A ne B

xs:string

xs:string

fn:not(op:numeric-equal(fn:compare(A, B), 0))

xs:boolean

A ne B

xs:date

xs:date

fn:not(op:date-equal(A, B))

xs:boolean

A ne B

xs:time

xs:time

fn:not(op:time-equal(A, B))

xs:boolean

A ne B

xs:dateTime

xs:dateTime

fn:not(op:dateTime-equal(A, B))

xs:boolean

A ne B

xs:duration

xs:duration

fn:not(op:duration-equal(A, B))

xs:boolean

A ne B

Gregorian

Gregorian

fn:not(op:gYear-equal(A, B)) etc.

xs:boolean

A ne B

xs:hexBinary

xs:hexBinary

fn:not(op:hexBinary--equal(A, B))

xs:boolean

A ne B

xs:base64Binary

xs:base64Binary

fn:not(op:base64Binary-equal(A, B))

xs:boolean

A ne B

xs:anyURI

xs:anyURI

fn:not(op:numeric-equal(fn:compare(A, B), 0))

xs:boolean

A ne B

xs:QName

xs:QName

fn:not(op:QName-equal(A, B))

xs:boolean

A ne B

xs:NOTATION

xs:NOTATION

fn:not(op:NOTATION-equal(A, B))

xs:boolean

A gt B

numeric

numeric

op:numeric-greater-than(A, B)

xs:boolean

A gt B

xs:boolean

xs:boolean

op:boolean-greater-than(A, B)

xs:boolean

A gt B

xs:string

xs:string

op:numeric-greater-than(fn:compare(A, B), 0)

xs:boolean

A gt B

xs:date

xs:date

op:date-greater-than(A, B)

xs:boolean

A gt B

xs:time

xs:time

op:time-greater-than(A, B)

xs:boolean

A gt B

xs:dateTime

xs:dateTime

op:dateTime-greater-than(A, B)

xs:boolean

A gt B

xs:yearMonthDuration

xs:yearMonthDuration

op:yearMonthDuration-greater-than(A, B)

xs:boolean

A gt B

xs:dayTimeDuration

xs:dayTimeDuration

op:dayTimeDuration-greater-than(A, B)

xs:boolean

A gt B

xs:anyURI

xs:anyURI

op:numeric-greater-than(fn:compare(A, B), 0)

xs:boolean

A lt B

numeric

numeric

op:numeric-less-than(A, B)

xs:boolean

A lt B

xs:boolean

xs:boolean

op:boolean-less-than(A, B)

xs:boolean

A lt B

xs:string

xs:string

op:numeric-less-than(fn:compare(A, B), 0)

xs:boolean

A lt B

xs:date

xs:date

op:date-less-than(A, B)

xs:boolean

A lt B

xs:time

xs:time

op:time-less-than(A, B)

xs:boolean

A lt B

xs:dateTime

xs:dateTime

op:dateTime-less-than(A, B)

xs:boolean

A lt B

xs:yearMonthDuration

xs:yearMonthDuration

op:yearMonthDuration-less-than(A, B)

xs:boolean

A lt B

xs:dayTimeDuration

xs:dayTimeDuration

op:dayTimeDuration-less-than(A, B)

xs:boolean

A lt B

xs:anyURI

xs:anyURI

op:numeric-less-than(fn:compare(A, B), 0)

xs:boolean

A ge B

numeric

numeric

op:numeric-greater-than(A, B) or op:numeric-equal(A, B)

xs:boolean

A ge B

xs:boolean

xs:boolean

fn:not(op:boolean-less-than(A, B))

xs:boolean

A ge B

xs:string

xs:string

op:numeric-greater-than(fn:compare(A, B), -1)

xs:boolean

A ge B

xs:date

xs:date

fn:not(op:date-less-than(A, B))

xs:boolean

A ge B

xs:time

xs:time

fn:not(op:time-less-than(A, B))

xs:boolean

A ge B

xs:dateTime

xs:dateTime

fn:not(op:dateTime-less-than(A, B))

xs:boolean

A ge B

xs:yearMonthDuration

xs:yearMonthDuration

fn:not(op:yearMonthDuration-less-than(A, B))

xs:boolean

A ge B

xs:dayTimeDuration

xs:dayTimeDuration

fn:not(op:dayTimeDuration-less-than(A, B))

xs:boolean

A ge B

xs:anyURI

xs:anyURI

op:numeric-greater-than(fn:compare(A, B), -1)

xs:boolean

A le B

numeric

numeric

op:numeric-less-than(A, B) or op:numeric-equal(A, B)

xs:boolean

A le B

xs:boolean

xs:boolean

fn:not(op:boolean-greater-than(A, B))

xs:boolean

A le B

xs:string

xs:string

op:numeric-less-than(fn:compare(A, B), 1)

xs:boolean

A le B

xs:date

xs:date

fn:not(op:date-greater-than(A, B))

xs:boolean

A le B

xs:time

xs:time

fn:not(op:time-greater-than(A, B))

xs:boolean

A le B

xs:dateTime

xs:dateTime

fn:not(op:dateTime-greater-than(A, B))

xs:boolean

A le B

xs:yearMonthDuration

xs:yearMonthDuration

fn:not(op:yearMonthDuration-greater-than(A, B))

xs:boolean

A le B

xs:dayTimeDuration

xs:dayTimeDuration

fn:not(op:dayTimeDuration-greater-than(A, B))

xs:boolean

A le B

xs:anyURI

xs:anyURI

op:numeric-less-than(fn:compare(A, B), 1)

xs:boolean

A is B

node()

node()

op:is-same-node(A, B)

xs:boolean

A << B

node()

node()

op:node-before(A, B)

xs:boolean

A >> B

node()

node()

op:node-after(A, B)

xs:boolean

A union B

node()*

node()*

op:union(A, B)

node()*

A | B

node()*

node()*

op:union(A, B)

node()*

A intersect B

node()*

node()*

op:intersect(A, B)

node()*

A except B

node()*

node()*

op:except(A, B)

node()*

A to B

xs:integer

xs:integer

op:to(A, B)

xs:integer*

A , B

item()*

item()*

op:concatenate(A, B)

item()*

Unary Operators

Operator

Operand type

Function

Result type

+ A

numeric

op:numeric-unary-plus(A)

numeric

- A

numeric

op:numeric-unary-minus(A)

numeric

C Context Components

The tables in this section describe how values are assigned to
the various components of the static context and dynamic context,
and to the parameters that control the serialization process.

C.1 Static Context
Components

The following table describes the components of the static
context. The following aspects of each component are
described:

Default initial value: This is the initial value of the
component if it is not overridden or augmented by the
implementation or by a query.

Can be overwritten or augmented by implementation:
Indicates whether an XQuery implementation is allowed to replace
the default initial value of the component by a different,
implementation-defined value
and/or to augment the default initial value by additional implementation-defined values.

Can be overwritten or augmented by a query: Indicates
whether a query is allowed to replace and/or augment the initial
value provided by default or by the implementation. If so,
indicates how this is accomplished (for example, by a declaration
in the prolog).

Scope: Indicates where the component is applicable.
"Global" indicates that the component applies globally, throughout
all the modules used in a query. "Module" indicates that the
component applies throughout a module. "Lexical" indicates that the component
applies within the expression in which it is defined (equivalent to
"module" if the component is declared in a Prolog.)

Consistency Rules: Indicates rules that must be
observed in assigning values to the component. Additional
consistency rules may be found in 2.2.5 Consistency
Constraints.

Static Context Components

Component

Default initial value

Can be overwritten or augmented by implementation?

Can be overwritten or augmented by a query?

Scope

Consistency rules

XPath 1.0 Compatibility Mode

false

no

no

global

Must be false.

Statically known namespaces

fn, xml, xs,
xsi, local

overwriteable and augmentable (except for
xml)

overwriteable and augmentable by prolog or element
constructor

lexical

Only one namespace can be assigned to a given prefix per
lexical scope.

Default element/type namespace

no namespace

overwriteable

overwriteable by prolog or element constructor

lexical

Only one default namespace per lexical scope.

Default function namespace

fn

overwriteable (not recommended)

overwriteable by prolog

module

None.

In-scope schema types

built-in types in xs

augmentable

augmentable by schema import in prolog

module

Only one definition per global or local type.

In-scope element declarations

none

augmentable

augmentable by schema import in prolog

module

Only one definition per global or local element name.

In-scope attribute declarations

none

augmentable

augmentable by schema import in prolog

module

Only one definition per global or local attribute name.

In-scope variables

none

augmentable

overwriteable and augmentable by prolog and by variable-binding
expressions

C.2 Dynamic Context
Components

The following table describes the components of the dynamic
context. The following aspects of each component are
described:

Default initial value: This is the initial value of the
component if it is not overridden or augmented by the
implementation or by a query.

Can be overwritten or augmented by implementation:
Indicates whether an XQuery implementation is allowed to replace
the default initial value of the component by a different implementation-defined value
and/or to augment the default initial value by additional implementation-defined values.

Can be overwritten or augmented by a query: Indicates
whether a query is allowed to replace and/or augment the initial
value provided by default or by the implementation. If so,
indicates how this is accomplished.

Scope: Indicates where the component is applicable.
"Global" indicates that the component applies globally, throughout
all the modules used in a query, and remains constant during
evaluation of a query. "Dynamic" indicates that evaluation of an
expression may influence the value of the component for that
expression and for nested expressions.

Consistency Rules: Indicates rules that must be
observed in assigning values to the component. Additional
consistency rules may be found in 2.2.5 Consistency
Constraints.

Dynamic Context Components

Component

Default initial value

Can be overwritten or augmented by implementation?

Can be overwritten or augmented by a query?

Scope

Consistency rules

Context item

none

overwriteable

overwritten during evaluation of path expressions and
predicates - initial value may be overwritten with a context item
declaration.

dynamic

None

Context position

none

overwriteable

overwritten during evaluation of path expressions and
predicates

dynamic

If context item is defined, context position must be >0 and
<= context size; else context position is undefined.

Context size

none

overwriteable

overwritten during evaluation of path expressions and
predicates

dynamic

If context item is defined, context size must be >0; else
context size is undefined.

Variable values

none

augmentable

overwriteable and augmentable by prolog and by variable-binding
expressions

Must include a timezone. Remains constant during evaluation of
a query.

Implicit timezone

none

must be initialized by implementation

no

global

Remains constant during evaluation of a query.

Available documents

none

must be initialized by implementation

no

global

None

Available collections

none

must be initialized by implementation

no

global

None

Default collection

none

overwriteable

no

global

None

C.3 Serialization
Parameters

The following table specifies default values for the parameters
that control the process of serializing an XDM instance into XML notation
(method = "xml"). The meanings of the various
parameters are defined in [XSLT and XQuery Serialization
1.1]. For each parameter, an XQuery implementation may (but is
not required to) allow a query to override the default value with
an option declaration, as discussed in 2.2.4 Serialization.

D Implementation-Defined Items

The circumstances in which warnings are raised, and the ways in which
warnings are handled.

The method by which errors are reported to the external
processing environment.

Whether the implementation is based on the rules of [XML 1.0] and [XML Names] or the
rules of [XML 1.1] and [XML Names 1.1]. One of these sets of rules must
be applied consistently by all aspects of the implementation. If
the implementation is based on the rules of [XML
1.0], the edition used must be at least Third Edition; the
edition used is implementation-defined, but we
recommend that implementations use the latest version.

ISO (International Organization for Standardization).
ISO/IEC 10646:2003. Information technology—Universal
Multiple-Octet Coded Character Set (UCS), as, from time to
time, amended, replaced by a new edition, or expanded by the
addition of new parts. [Geneva]: International Organization for
Standardization. (See http://www.iso.org for the latest
version.)

Unicode

The Unicode Consortium. The Unicode Standard Reading,
Mass.: Addison-Wesley, 2003, as updated from time to time by the
publication of new versions. See http://www.unicode.org/unicode/standard/versions
for the latest version and additional information on versions of
the standard and of the Unicode Character Database. The version of
Unicode to be used is implementation-defined, but
implementations are recommended to use the latest Unicode
version.

XML
1.0

World Wide Web Consortium. Extensible Markup Language
(XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/REC-xml.
The edition of XML 1.0 must be no earlier than the Third Edition;
the edition used is implementation-defined, but we
recommend that implementations use the latest version.

XQuery and XPath
Data Model (XDM) 1.1, Norman Walsh, John Snelson,
Editors. World Wide Web Consortium, 15 December 2009. This version
is http://www.w3.org/TR/2009/WD-xpath-datamodel-11-20091215/. The
latest
version is available at
http://www.w3.org/TR/xpath-datamodel-11/.

XSLT and
XQuery Serialization 1.1, Henry Zongaro, Editor. World
Wide Web Consortium, 15 December 2009. This version is
http://www.w3.org/TR/2009/WD-xslt-xquery-serialization-11-20091215/.
The latest
version is available at
http://www.w3.org/TR/xslt-xquery-serialization-11/.

E.2 Non-normative References

XQuery
1.1 Requirements

XQuery 1.1
Requirements, Daniel Engovatov, Jonathan Robie, Editors.
World Wide Web Consortium, 15 December 2009. This version
is http://www.w3.org/TR/2009/WD-xquery-11-requirements-20091215/.
The latest
version is available at
http://www.w3.org/TR/xquery-11-requirements/.

XML Path Language (XPath)
2.1

XML Path Language (XPath)
2.1, Jonathan Robie, Don Chamberlin, Michael Dyck, John
Snelson, Editors. World Wide Web Consortium, 15 December 2009. This
version is http://www.w3.org/TR/2009/WD-xpath-21-20091215/. The
latest version is
available at http://www.w3.org/TR/xpath-21/.

XQuery 1.0 and XPath 2.0 Formal
Semantics

XQuery
1.0 and XPath 2.0 Formal Semantics, Jérôme Siméon,
Denise Draper, Peter Frankhauser, et. al., Editors. World
Wide Web Consortium, 23 January 2007. This version is
http://www.w3.org/TR/2007/REC-xquery-semantics-20070123/. The
latest version
is available at http://www.w3.org/TR/xquery-semantics/.

XQueryX 1.1

XQueryX 1.1,
Jim Melton, Editor. World Wide Web Consortium, 15 December 2009.
This version is http://www.w3.org/TR/2009/WD-xqueryx-11-20091215/.
The latest version
is available at http://www.w3.org/TR/xqueryx-11/.

XSL
Transformations (XSLT) Version 2.1

XSL
Transformations (XSLT) Version 2.1, Michael Kay, Editor.
World Wide Web Consortium, «awaiting First Public Working Draft
publication». This version is
http://www.w3.org/TR/2007/WD-xslt-21-YYYYMMDD/. The latest version is available at
http://www.w3.org/TR/xslt-21/.

During the analysis phase, it is a static error if the static type assigned to an expression
other than the expression () or data(())
is empty-sequence().

err:XPTY0006

(Not currently used.)

err:XPTY0007

(Not currently used.)

err:XPST0008

It is a static
error if an expression refers to an element name, attribute
name, schema type name, namespace prefix, or variable name that is
not defined in the static context, except for an ElementName
in an ElementTest or an
AttributeName in an AttributeTest.

err:XQST0009

An implementation that does not support the Schema Import
Feature must raise a static error if a Prolog contains a schema
import.

err:XPST0010

An implementation must raise a static error if it encounters a reference to
an axis that it does not support.

err:XQST0012

It is a static
error if the set of definitions contained in all schemas
imported by a Prolog do not satisfy the conditions for schema
validity specified in Sections 3 and 5 of [XML
Schema] Part 1--i.e., each definition must be valid, complete,
and unique.

err:XQST0013

It is a static
error if an implementation recognizes a pragma but determines
that its content is invalid.

It is a type
error if the content sequence in an element constructor
contains an attribute node following a node that is not an
attribute node.

err:XQDY0025

It is a dynamic error if any attribute of a
constructed element does not have a name that is distinct from the
names of all other attributes of the constructed element.

err:XQDY0026

It is a dynamic error if the result of the content
expression of a computed processing instruction constructor
contains the string "?>".

err:XQDY0027

In a validate expression, it is a dynamic error if the root element
information item in the PSVI resulting from validation does not
have the expected validity property: valid if
validation mode is strict, or either
valid or notKnown if validation mode is
lax.

err:XQTY0028

(Not currently used.)

err:XQDY0029

(Not currently used.)

err:XQTY0030

It is a type
error if the argument of a validate expression
does not evaluate to exactly one document or element node.

err:XQST0031

It is a static
error if the version number specified in a version declaration
is not supported by the implementation.

It is a static
error for a function declaration to have more than one
parameter with the same name.

err:XQST0040

It is a static
error if the attributes specified by a direct element
constructor do not have distinct expanded QNames.

err:XQDY0041

It is a dynamic error if the value of the name
expression in a computed processing instruction constructor cannot
be cast to the type xs:NCName.

err:XQST0042

(Not currently used.)

err:XQST0043

(Not currently used.)

err:XQDY0044

It is a static
error the node-name of a node constructed by a computed
attribute constructor has any of the following properties:

Its namespace prefix is xmlns.

It has no namespace prefix and its local name is
xmlns.

Its namespace URI is
http://www.w3.org/2000/xmlns/.

Its namespace prefix is xml and its namespace URI
is not http://www.w3.org/XML/1998/namespace.

Its namespace prefix is other than xml and its
namespace URI is
http://www.w3.org/XML/1998/namespace.

err:XQST0045

It is a static
error if the function name in a function declaration is in one
of the following namespaces:
http://www.w3.org/XML/1998/namespace,
http://www.w3.org/2001/XMLSchema,
http://www.w3.org/2001/XMLSchema-instance,
http://www.w3.org/2005/xpath-functions.

err:XQST0046

An implementation MAY raise a
static error if
the value of a URILiteral is
of nonzero length and is not in the lexical space of
xs:anyURI.

err:XQST0047

It is a static
error if multiple module imports in the same Prolog specify the
same target namespace.

err:XQST0048

It is a static
error if a function or variable declared in a library module is
not in the target namespace of the library module.

err:XQST0049

It is a static
error if two or more variables declared or imported by a
module have equal expanded
QNames (as defined by the eq operator.)

err:XPDY0050

It is a dynamic error if the dynamic type of the
operand of a treat expression does not match the
sequence type
specified by the treat expression. This error might
also be raised by a path expression beginning with "/"
or "//" if the context node is not in a tree that is
rooted at a document node. This is because a leading
"/" or "//" in a path expression is an
abbreviation for an initial step that includes the clause
treat as document-node().

It is a static
error if a schema import binds a namespace prefix but does not
specify a target namespace other than a zero-length string.

err:XQST0058

It is a static
error if multiple schema imports specify the same target
namespace.

err:XQST0059

It is a static
error if an implementation is unable to process a schema or
module import by finding a schema or module with the specified
target namespace.

err:XQST0060

It is a static
error if the name of a function in a function declaration is
not in a namespace (expanded QName has a null namespace URI).

err:XQDY0061

It is a dynamic error if the operand of a validate
expression is a document node whose children do not consist of
exactly one element node and zero or more comment and processing
instruction nodes, in any order.

err:XQDY0062

(Not currently used.)

err:XQST0063

(Not currently used.)

err:XQDY0064

It is a dynamic error if the value of the name
expression in a computed processing instruction constructor is
equal to "XML" (in any combination of upper and lower case).

A static
error is raised if one of the predefined prefixes
xml or xmlns appears in a namespace
declaration, or if any of the following conditions is statically
detected in any expression or declaration:

The prefix xml is bound to some namespace URI other
than http://www.w3.org/XML/1998/namespace.

A prefix other than xml is bound to the namespace
URI http://www.w3.org/XML/1998/namespace.

The prefix xmlns is bound to any namespace URI.

A prefix other than xmlns is bound to the namespace
URI http://www.w3.org/2000/xmlns/.

err:XQST0071

A static
error is raised if the namespace declaration attributes of a
direct element constructor do not have distinct names.

err:XQDY0072

It is a dynamic error if the result of the content
expression of a computed comment constructor contains two adjacent
hyphens or ends with a hyphen.

An implementation MAY raise a
dynamic error
if an xml:id error, as defined in [XML ID], is encountered during construction of an
attribute named xml:id.

err:XQDY0092

An implementation MAY raise a
dynamic error
if a constructed attribute named xml:space has a value
other than preserve or default.

err:XQST0094

In the group by clause of a FLWOR expression, it is
a static error
if the name of a grouping variable is not equal (by the
eq operator on expanded QNames) to the name of a
variable that is bound by a for or let
clause that precedes the group by clause.

err:XQDY0095

In the group by clause of a FLWOR expression, it is
a dynamic
error if the value bound to a grouping variable consists of a
sequence of more than one item.

err:XQST0096

It is a dynamic error the node-name of a node
constructed by a computed element constructor has any of the
following properties:

Its namespace prefix is xmlns.

Its namespace URI is
http://www.w3.org/2000/xmlns/.

Its namespace prefix is xml and its namespace URI
is not http://www.w3.org/XML/1998/namespace.

Its namespace prefix is other than xml and its
namespace URI is
http://www.w3.org/XML/1998/namespace.

An error is raised if the namespace URI in a computed namespace
constructor is bound to the predefined prefix xmlns,
or if a namespace URI other than
http://www.w3.org/XML/1998/namespace is bound to the
prefix xml, or if the prefix xml is bound
to a namespace URI other than
http://www.w3.org/XML/1998/namespace.

err:XQTY0102

In an element constructor, if two or more namespace bindings in
the in-scope bindings would have the same prefix, then an error is
raised if they have different URIs; if they would have the same
prefix and URI, duplicate bindings are ignored.

It is a static
error if the local name of an output declaration in the
http://www.w3.org/2009/xquery-serialization namespace
is not one of the serialization parameter names listed in C.3 Serialization
Parameters.

G The
application/xquery Media Type

This Appendix specifies the media type for XQuery Version 1.0.
XQuery is a language for querying over collections of data from XML
data sources, as specified in the main body of this document. This
media type is being submitted to the IESG (Internet Engineering
Steering Group) for review, approval, and registration with IANA
(Internet Assigned Numbers Authority.)

G.1
Introduction

This document, found at http://www.w3.org/TR/xquery/,
together with its normative references, defines the language XQuery
Version 1.0. This Appendix provides information about the
application/xquery media type, which is intended to be
used for transmitting queries written in the XQuery language.

G.2 Registration of MIME Media
Type application/xquery

MIME media type name: application

MIME subtype name: xquery

Required parameters: none

Optional parameters: none

The syntax of XQuery is expressed in Unicode but may be written
with any Unicode-compatible character encoding, including UTF-8 or
UTF-16, or transported as US-ASCII or ISO-8859-1 with Unicode
characters outside the range of the given encoding represented
using an XML-style &#xddd; syntax.

G.2.1 Interoperability
Considerations

None known.

G.2.2 Applications Using this
Media Type

The public XQuery Web
page lists more than two dozen implementations of the XQuery
language, both proprietary and open source.

This new media type is being registered to allow for deployment
of XQuery on the World Wide Web.

G.2.3
File Extensions

The most common file extensions in use for XQuery are
.xq and .xquery.

The appropriate Macintosh file type code is
TEXT.

G.2.4
Intended Usage

The intended usage of this media type is for interchange of
XQuery expressions.

G.2.5 Author/Change
Controller

XQuery was produced by, and is maintained by, the World Wide Web
Consortium's XML Query Working Group. The W3C has change control
over this specification.

G.3 Encoding Considerations

For use with transports that are not 8-bit clean,
quoted-printable encoding is recommended since the XQuery syntax
itself uses the US-ASCII-compatible subset of Unicode.

G.4 Recognizing XQuery Files

An XQuery file may have the string xquery version
"V.V" near the beginning of the document, where
"V.V" is a version number. Currently the version
number, if present, must be "1.0".

G.5 Charset Default Rules

XQuery documents use the Unicode character set and, by default,
the UTF-8 encoding.

G.6 Security Considerations

Queries written in XQuery may cause arbitrary URIs or IRIs to be
dereferenced. Therefore, the security issues of [RFC3987] Section 8 should be considered. In
addition, the contents of resources identified by
file: URIs can in some cases be accessed, processed
and returned as results. XQuery expressions can invoke any of the
functions defined in [XQuery and
XPath Functions and Operators 1.1]. For example, the
fn:doc() and fn:doc-available() functions
allow local filesystem probes as well as access to any URI-defined
resource accessible from the system evaluating the XQuery
expression.

Available collections. This is a mapping of strings onto
sequences of nodes. The string represents the absolute URI of a
resource. The sequence of nodes represents the result of the
fn:collection function when that URI is supplied as
the argument.

available documents

Available documents. This is a mapping of strings onto
document nodes. The string represents the absolute URI of a
resource. The document node is the root of a tree that represents
that resource using the data model. The document node is returned by
the fn:doc function when applied to that URI.

axis step

An axis step returns a sequence of nodes that are
reachable from the context node via a specified axis. Such a step
has two parts: an axis, which defines the "direction of
movement" for the step, and a node test, which selects nodes based on their
kind, name, and/or type annotation.

base URI

Base URI. This is an absolute URI, used when necessary in
the resolution of relative URIs (for example, by the
fn:resolve-uri function.)

Construction mode. The construction mode governs the
behavior of element and document node constructors. If construction
mode is preserve, the type of a constructed element
node is xs:anyType, and all attribute and element
nodes copied during node construction retain their original types.
If construction mode is strip, the type of a
constructed element node is xs:untyped; all element
nodes copied during node construction receive the type
xs:untyped, and all attribute nodes copied during node
construction receive the type xs:untypedAtomic.

constructor function

The constructor function for a given type is used to
convert instances of other atomic types into the given type. The
semantics of the constructor function call T($arg) are
defined to be equivalent to the expression (($arg) cast as
T?).

content expression

The final part of a computed constructor is an expression
enclosed in braces, called the content expression of the
constructor, that generates the content of the node.

context
item

The context item is the item currently being processed.
An item is either an atomic value or a node.

context item static type

Context item static type. This component defines the
static type of
the context item within the scope of a given expression.

context
node

When the context item is a node, it can also be referred to as
the context node.

context position

The context position is the position of the context item
within the sequence of items currently being processed.

context
size

The context size is the number of items in the sequence
of items currently being processed.

copy-namespaces declaration

A copy-namespaces declaration sets the value of copy-namespaces mode in the
static
context, overriding any implementation-defined default.
Copy-namespaces mode controls the namespace bindings that are
assigned when an existing element node is copied by an element
constructor or document constructor.

copy-namespaces mode

Copy-namespaces mode. This component controls the
namespace bindings that are assigned when an existing element node
is copied by an element constructor, as described in 3.7.1 Direct Element
Constructors. Its value consists of two parts:
preserve or no-preserve, and
inherit or no-inherit.

current
dateTime

Current dateTime. This information represents an
implementation-dependent point
in time during the processing of a
query, and includes an explicit timezone. It can be
retrieved by the fn:current-dateTime function. If
invoked multiple times during the execution of a query, this function always returns the same
result.

data
model

XQuery 1.1 operates on the abstract, logical structure of an XML
document, rather than its surface syntax. This logical structure,
known as the data model, is defined in [XQuery and XPath Data Model (XDM)
1.1].

data model schema

For a given node in an XDM instance, the data model
schema is defined as the schema from which the type annotation of
that node was derived.

decimal-separator specifies the character used for the
decimal-separator-sign; the default value is the period character
(.)

default collation

Default collation. This identifies one of the collations
in statically known collations as the
collation to be used by functions and operators for comparing and
ordering values of type xs:string and
xs:anyURI (and types derived from them) when no
explicit collation is specified.

Default collection. This is the sequence of nodes that
would result from calling the fn:collection function
with no arguments.

default element/type namespace

Default element/type namespace. This is a namespace URI
or "none". The namespace URI, if present, is used for any
unprefixed QName appearing in a position where an element or type
name is expected.

default
function namespace

Default function namespace. This is a namespace URI or
"none". The namespace URI, if present, is used for any unprefixed
QName appearing in a position where a function name is
expected.

default order for empty
sequences

Default order for empty sequences. This component
controls the processing of empty sequences and NaN
values as ordering keys in an order by clause in a
FLWOR expression, as described in 3.8.8 Order By Clause.

A dynamic type is associated with each value as it is
computed. The dynamic type of a value may be more specific than the
static type of
the expression that computed it (for example, the static type of an
expression might be xs:integer*, denoting a sequence
of zero or more integers, but at evaluation time its value may have
the dynamic type xs:integer, denoting exactly one
integer.)

The effective case in a switch expression is the first
case clause in which the value of the switch operand expression is
equivalent to the value of a case operand, as defined in equivalence of two atomic
values, or the default clause if no such case clause
exists.

effective case

The effective case in a typeswitch
expression is the first case clause such that the
value of the operand expression matches the SequenceType in the
case clause, using the rules of SequenceType matching.

empty order declaration

An empty order declaration sets the default order for empty sequences in
the static
context, overriding any implementation-defined default. This
declaration controls the processing of empty sequences and
NaN values as ordering keys in an order
by clause in a FLWOR expression.

empty sequence

A sequence containing zero items is called an empty
sequence.

encoding declaration

If present, a version declaration may optionally include an
encoding declaration. The value of the string literal
following the keyword encoding is an encoding name,
and must conform to the definition of EncName
specified in [XML 1.0] [err:XQST0087]. The purpose of an encoding
declaration is to allow the writer of a query to provide a string
that indicates how the query is encoded, such as
"UTF-8", "UTF-16", or
"US-ASCII".

equivalence of two atomic
values

Equivalence of two atomic valuesV1 and
V2 is defined by the following equivalence rules:

External functions are functions that are implemented
outside the query environment.

filter expression

A filter expression consists simply of a primary
expression followed by zero or more predicates. The result of the filter expression
consists of the items returned by the primary expression, filtered
by applying each predicate in turn, working from left to right.

focus

The first three components of the dynamic context (context item,
context position, and context size) are called the focus of
the expression.

function conversion rules

The function conversion rules are used to convert an
argument value or a return value to its
expected type; that is, to the declared type of the function
parameter or return.

Function item coercion wraps a function
itemDM11 in a new inline function with
signature the same as the expected type. This effectively delays
the checking of the argument and return types until the function
item is invoked.

function signature

Function signatures. This component defines the set of
functions that are available to be called from within an
expression. Each function is uniquely identified by its expanded QName and
its arity (number of parameters).

Gregorian

In the operator mapping tables, the term Gregorian refers
to the types xs:gYearMonth, xs:gYear,
xs:gMonthDay, xs:gDay, and
xs:gMonth.

Implementation-defined indicates an aspect that may
differ between implementations, but must be specified by the
implementor for each particular implementation.

implementation dependent

Implementation-dependent indicates an aspect that may
differ between implementations, is not specified by this or any W3C
specification, and is not required to be specified by the
implementor for any particular implementation.

implicit
timezone

Implicit timezone. This is the timezone to be used when a
date, time, or dateTime value that does not have a timezone is used
in a comparison or arithmetic operation. The implicit timezone is
an implementation-defined value of
type xs:dayTimeDuration. See [XML
Schema] for the range of legal values of a timezone.

infinity

infinity specifies the string used for the
infinity-symbol; the default value is the string Infinity

initializing expression

If a variable declaration includes an expression
(VarValue or VarDefaultValue), the
expression is called an initializing expression. The static
context for an initializing expression includes all functions,
variables, and namespaces that are declared or imported anywhere in
the Prolog, other than the variable being declared.

In-scope attribute declarations. Each attribute
declaration is identified either by an expanded QName (for a top-level
attribute declaration) or by an implementation-dependent
attribute identifier (for a local attribute declaration).
If the Schema Import Feature is supported,
in-scope attribute declarations include all attribute declarations
found in imported schemas.

in-scope element
declarations

In-scope element declarations. Each element declaration
is identified either by an expanded QName (for a top-level element
declaration) or by an implementation-dependent element
identifier (for a local element declaration). If the Schema Import Feature is supported,
in-scope element declarations include all element declarations
found in imported schemas.

in-scope namespaces

The in-scope namespaces property of an element node is a
set of namespace bindings, each of which associates a
namespace prefix with a URI, thus defining the set of namespace
prefixes that are available for interpreting QNames within the
scope of the element. For a given element, one namespace binding
may have an empty prefix; the URI of this namespace binding is the
default namespace within the scope of the element.

in-scope schema
definitions

In-scope schema definitions. This is a generic term for
all the element declarations, attribute declarations, and schema
type definitions that are in scope during processing of an
expression.

In-scope variables. This is a set of (expanded QName,
type) pairs. It defines the set of variables that are available for
reference within an expression. The expanded QName is the name of the
variable, and the type is the static type of the variable.

MUST means that the item is an absolute requirement of
the specification.

named
function

A named function is a function defined in the static
context for the query. To uniquely identify a particular named
function, both its name as a QName and its arity are required.

name expression

When an expression is used to specify the name of a constructed
node, that expression is called the name expression of the
constructor.

namespace declaration

A namespace declaration declares a namespace prefix and
associates it with a namespace URI, adding the (prefix, URI) pair
to the set of statically known namespaces.

namespace declaration attribute

A namespace declaration attribute is used inside a direct
element constructor. Its purpose is to bind a namespace prefix or
to set the default element/type namespace for the
constructed element node, including its attributes.

namespace-sensitive

A value is namespace-sensitive if it includes an item
whose dynamic
type is xs:QName or xs:NOTATION or is
derived by restriction from xs:QName or
xs:NOTATION.

name test

A node test that consists only of a QName or a Wildcard is
called a name test.

NaN

NaN specifies the string used for the NaN-symbol, which
is used to represent the value NaN (not-a-number); the default
value is the string NaN

A nondeterministic function is a function that is not
guaranteed to always return the same result when it is invoked with
the same arguments.

numeric

When referring to a type, the term numeric denotes the
types xs:integer, xs:decimal,
xs:float, and xs:double.

numeric predicate

A predicate whose predicate expression returns a numeric type is
called a numeric predicate.

operator function

For each operator and valid combination of operand types, the
operator mapping tables specify a result type and an operator
function that implements the semantics of the operator for the
given types.

option declaration

An option declaration declares an option that affects the
behavior of a particular implementation. Each option consists of an
identifying QName and a StringLiteral.

ordering mode

Ordering mode. Ordering mode, which has the value
ordered or unordered, affects the
ordering of the result sequence returned by certain path expressions,
FLWOR expressions, and union, intersect,
and except expressions.

An output declaration is an option declaration in the
predeclared namespace associated with the output
prefix; it is used to declare an output parameter for serializing
the output of the query.

path expression

A path expression can be used to locate nodes within
trees. A path expression consists of a series of one or more
steps, separated by
"/" or "//", and optionally beginning
with "/" or "//".

pattern-separator-sign

pattern-separator-sign specifies the character used for
the pattern-separator-sign, which separates positive and negative
sub-pictures in a picture string; the default value is the
semi-colon character (;)

percent-sign

percent-sign specifies the character used for the
percent-sign; the default value is the percent character (%)

per-mille-sign

per-mille-sign specifies the character used for the
per-mille-sign; the default value is the Unicode per-mille
character (#x2030)

positional variable

A positional variable is a variable that is preceded by
the keyword at.

pragma

A pragma is denoted by the delimiters (# and
#), and consists of an identifying QName followed by
implementation-defined
content.

predefined entity
reference

A predefined entity reference is a short sequence of
characters, beginning with an ampersand, that represents a single
character that might otherwise have syntactic significance.

predicate

A predicate consists of an expression, called a
predicate expression, enclosed in square brackets. A
predicate serves to filter a sequence, retaining some items and
discarding others.

primary expression

Primary expressions are the basic primitives of the
language. They include literals, variable references, context item
expressions, constructors, and function
calls. A primary expression may also be created by enclosing any
expression in parentheses, which is sometimes helpful in
controlling the precedence of operators.

principal node kind

Every axis has a principal node kind. If an axis can
contain elements, then the principal node kind is element;
otherwise, it is the kind of nodes that the axis can contain.

The Query Body, if present, consists of an expression
that defines the result of the query.

reverse document order

The node ordering that is the reverse of document order is
called reverse document order.

schema
import

A schema import imports the element declarations,
attribute declarations, and type definitions from a schema into the
in-scope
schema definitions. For each user-defined atomic type in
the schema, schema import also adds a corresponding constructor
function.

schema import feature

The Schema Import Feature permits the query Prolog to
contain a schema
import.

schema
type

A schema type is a type that is (or could be) defined
using the facilities of [XML Schema]
(including the built-in types of [XML
Schema]).

A sequence type is a type that can be expressed using the
SequenceType syntax.
Sequence types are used whenever it is necessary to refer to a type
in an XQuery 1.1 expression. The term sequence type suggests
that this syntax is used to describe the type of an XQuery 1.1
value, which is always a sequence.

SequenceType matching

During evaluation of an expression, it is sometimes necessary to
determine whether a value with a known dynamic type "matches" an expected
sequence
type. This process is known as SequenceType
matching.

serialization

Serialization is the process of converting an XDM instance into
a sequence of octets (step DM4 in Figure 1.)

serialization feature

A conforming XQuery implementation that supports the
Serialization FeatureMUST
provide means for serializing the result of a query, as specified
in 2.2.4 Serialization.

setter

Setters are declarations that set the value of some
property that affects query processing, such as construction mode,
ordering mode, or default collation.

should

SHOULD means that there may exist valid reasons in
particular circumstances to ignore a particular item, but the full
implications must be understood and carefully weighed before
choosing a different course.

singleton

A sequence containing exactly one item is called a
singleton.

stable

Document order is stable, which means that the relative
order of two nodes will not change during the processing of a given
query, even if this order is implementation-dependent.

statically known collations

Statically known collations. This is an implementation-defined set of
(URI, collation) pairs. It defines the names of the collations that
are available for use in processing queries
and expressions.

statically known collections

Statically known collections. This is a mapping from
strings onto types. The string represents the absolute URI of a
resource that is potentially available using the
fn:collection function. The type is the type of the
sequence of nodes that would result from calling the
fn:collection function with this URI as its
argument.

statically known decimal
formats

Statically known decimal formats. This is the set of
known decimal formats. Each format is used for serializing decimal
numbers using fn:format-number().

statically known default
collection type

Statically known default collection type. This is the
type of the sequence of nodes that would result from calling the
fn:collection function with no arguments.

statically
known documents

Statically known documents. This is a mapping from
strings onto types. The string represents the absolute URI of a
resource that is potentially available using the
fn:doc function. The type is the static type of a call to
fn:doc with the given URI as its literal argument.

statically known namespaces

Statically known namespaces. This is a set of (prefix,
URI) pairs that define all the namespaces that are known during
static processing of a given expression.

static analysis phase

The static analysis phase depends on the expression
itself and on the static context. The static analysis
phase does not depend on input data (other than schemas).

static context

The static context of an expression is the information
that is available during static analysis of the expression, prior
to its evaluation.

static
error

A static error is an error that must be detected during
the static analysis phase. A syntax error is an example of a
static
error.

static
type

The static type of an expression is the best inference
that the processor is able to make statically about the type of the
result of the expression.

A step is a part of a path expression that generates a sequence
of items and then filters the sequence by zero or more predicates. The value of the
step consists of those items that satisfy the predicates, working
from left to right. A step may be either an axis step or a filter
expression.

string
value

The string value of a node is a string and can be
extracted by applying the fn:string function to the
node.

substitution group

Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. Informally,
the substitution group headed by a given element (called the
head element) consists of the set of elements that can be
substituted for the head element without affecting the outcome of
schema validation.

subtype

A sequence
typeA is a subtype of a sequence type
B if and only if, for every value V, if
V matches A according to the rules of
SequenceType matching, then
V also matches B.

subtype substitution

The use of a value whose dynamic type is derived from an expected
type is known as subtype substitution.

symbol

Each rule in the grammar defines one symbol, using the
following format:

symbol ::= expression

symbol
separators

Whitespace and
Comments function as symbol
separators. For the most part, they are not mentioned in the
grammar, and may occur between any two terminal symbols mentioned
in the grammar, except where that is forbidden by the /* ws: explicit */ annotation in the EBNF, or by
the /* xgc: xml-version */
annotation.

target namespace

Each imported schema or module is identified by its target
namespace, which is the namespace of the objects (such as
elements or functions) that are defined by the schema or
module.

terminal

A terminal is a symbol or string or pattern that can
appear in the right-hand side of a rule, but never appears on the
left hand side in the main grammar, although it may appear on the
left-hand side of a rule in the grammar for terminals.

tuple

A tuple is a set of zero or more named variables, each of
which is bound to a value that is an XDM instance.

A variable binding may be accompanied by a type
declaration, which consists of the keyword as
followed by the static type of the variable, declared using the
syntax in 2.5.3 SequenceType
Syntax.

typed
value

The typed value of a node is a sequence of atomic values
and can be extracted by applying the fn:data function
to the node.

type
error

A type error may be raised during the static analysis
phase or the dynamic evaluation phase. During the static analysis
phase, a type error
occurs when the static type of an expression does not match
the expected type of the context in which the expression occurs.
During the dynamic evaluation phase, a type error occurs when the dynamic type of a value
does not match the expected type of the context in which the value
occurs.

In certain situations a value is said to be undefined
(for example, the value of the context item, or the typed value of
an element node). This term indicates that the property in question
has no value and that any attempt to use its value results in an
error.

URI

Within this specification, the term URI refers to a
Universal Resource Identifier as defined in [RFC3986] and extended in [RFC3987] with the new name IRI.

user-defined function

User defined functions are functions that contain a
function body, which provides the implementation of the
function as an XQuery expression.

Variable values. This is a set of (expanded QName, value)
pairs. It contains the same expanded QNames as the in-scope
variables in the static context for the expression. The
expanded QName is the name of the variable and the value is the
dynamic value of the variable, which includes its dynamic type.

version declaration

A version declaration can identify the applicable XQuery
syntax and semantics for a module, as well as its encoding.

The term XDM instance is used, synonymously with the term
value, to denote an unconstrained sequence of nodes and/or atomic values in the data model.

XPath 1.0 compatibility mode

XPath 1.0 compatibility mode.This
component must be set by all host languages that include XPath 2.1
as a subset, indicating whether rules for compatibility with XPath
1.0 are in effect. XQuery sets the value of this component to
false.

XQuery 1.0 Processor

An XQuery 1.0 Processor processes a query according to
the XQuery 1.0 specification.

XQuery 1.1 Processor

An XQuery 1.1 Processor processes a query according to
the XQuery 1.1 specification.

xs:anyAtomicType

xs:anyAtomicType is an atomic type that includes
all atomic values (and no values that are not atomic). Its base
type is xs:anySimpleType from which all simple types,
including atomic, list, and union types, are derived. All primitive
atomic types, such as xs:decimal and
xs:string, have xs:anyAtomicType as their
base type.

xs:dayTimeDuration

xs:dayTimeDuration is derived by restriction from
xs:duration. The lexical representation of
xs:dayTimeDuration is restricted to contain only day,
hour, minute, and second components.

xs:untyped

xs:untyped is used as the type annotation of
an element node that has not been validated, or has been validated
in skip mode.

xs:untypedAtomic

xs:untypedAtomic is an atomic type that is used to
denote untyped atomic data, such as text that has not been assigned
a more specific type.

xs:yearMonthDuration

xs:yearMonthDuration is derived by restriction from
xs:duration. The lexical representation of
xs:yearMonthDuration is restricted to contain only
year and month components.

zero-digit

zero-digit specifies the character used for the
digit-zero-sign; the default value is the digit zero (0). This
character must be a digit (category Nd in the Unicode property
database), and it must have the numeric value zero. This attribute
implicitly defines the Unicode character that is used to represent
each of the values 0 to 9 in the final result string: Unicode is
organized so that each set of decimal digits forms a contiguous
block of characters in numerical sequence.

I Example Applications
(Non-Normative)

This section contains examples of several important classes of
queries that can be expressed using XQuery. The applications
described here include joins across multiple data sources, grouping
and aggregation, queries based on sequential relationships,
recursive transformations, and selection of distinct combinations
of values.

Note:

This section needs to be rewritten in light of the new features
of XQuery 1.1, which can significantly simplify some of these
queries.

I.1 Joins

Joins, which combine data from multiple sources into a single
result, are a very important type of query. In this section we will
illustrate how several types of joins can be expressed in XQuery.
We will base our examples on the following three documents:

A document named parts.xml that contains many
part elements; each part element in turn
contains partno and description
subelements.

A document named suppliers.xml that contains many
supplier elements; each supplier element
in turn contains suppno and suppname
subelements.

A document named catalog.xml that contains
information about the relationships between suppliers and parts.
The catalog document contains many item elements, each
of which in turn contains partno, suppno,
and price subelements.

A conventional ("inner") join returns information from two or
more related sources, as illustrated by the following example,
which combines information from three documents. The example
generates a "descriptive catalog" derived from the catalog
document, but containing part descriptions instead of part numbers
and supplier names instead of supplier numbers. The new catalog is
ordered alphabetically by part description and secondarily by
supplier name.

The previous query returns information only about parts that
have suppliers and suppliers that have parts. An outer join
is a join that preserves information from one or more of the
participating sources, including elements that have no matching
element in the other source. For example, a left outer join
between suppliers and parts might return information about
suppliers that have no matching parts.

The following query demonstrates a left outer join. It returns
names of all the suppliers in alphabetic order, including those
that supply no parts. In the result, each supplier element contains
the descriptions of all the parts it supplies, in alphabetic
order.

The previous query preserves information about suppliers that
supply no parts. Another type of join, called a full outer
join, might be used to preserve information about both
suppliers that supply no parts and parts that have no supplier. The
result of a full outer join can be structured in any of several
ways. The following query generates a list of supplier
elements, each containing nested part elements for the
parts that it supplies (if any), followed by a list of
part elements for the parts that have no supplier.
This might be thought of as a "supplier-centered" full outer join.
Other forms of outer join queries are also possible.

The previous query uses an element constructor to enclose its
output inside a master-list element. The concatenation
operator (",") is used to combine the two main parts of the query.
The result is an ordered sequence of supplier elements
followed by an orphan-parts element that contains
descriptions of all the parts that have no supplier.

I.2 Queries on Sequence

XQuery uses the << and >>
operators to compare nodes based on document order. Although these
operators are quite simple, they can be used to express complex
queries for XML documents in which sequence is meaningful. The
first two queries in this section involve a surgical report that
contains procedure, incision,
instrument, action, and
anesthesia elements.

The following query returns all the action elements
that occur between the first and second incision
elements inside the first procedure. The original document order
among these nodes is preserved in the result of the query.

It is worth noting here that document order is defined in such a
way that a node is considered to precede its descendants in
document order. In the surgical report, an action is
never part of an incision, but an
instrument is. Since the >>
operator is based on document order, the predicate $i
>> ($proc//incision)[1] is true for any
instrument element that is a descendant of the first
incision element in the first procedure.

For some queries, it may be helpful to define a function that
can test whether a node precedes another node without being its
ancestor. The following function returns true if its
first operand precedes its second operand but is not an ancestor of
its second operand; otherwise it returns false:

Using the local:precedes function, we can write a
query that finds instrument elements between the first
two incisions, excluding from the query result any
instrument that is a descendant of the first
incision:

The following query reports incisions for which no prior
anesthesia was recorded in the surgical report. Since an
anesthesia is never part of an incision,
we can use << instead of the less-efficient
local:precedes function:

for $proc in /report/procedure
where some $i in $proc//incision satisfies
fn:empty($proc//anesthesia[. << $i])
return $proc

In some documents, particular sequences of elements may indicate
a logical hierarchy. This is most commonly true of HTML. The
following query returns the introduction of an XHTML document,
wrapping it in a div element. In this example, we
assume that an h2 element containing the text
"Introduction" marks the beginning of the introduction, and the
introduction continues until the next h2 or
h1 element, or the end of the document, whichever
comes first.

Note that the above query makes explicit the hierarchy that was
implicit in the original document. In this example, we assume that
the h2 element containing the text "Introduction" has
no subelements.

I.3 Recursive
Transformations

Occasionally it is necessary to scan over a hierarchy of
elements, applying some transformation at each level of the
hierarchy. In XQuery this can be accomplished by defining a
recursive function. In this section we will present two examples of
such recursive functions.

Suppose that we need to compute a table of contents for a given
document by scanning over the document, retaining only elements
named section or title, and preserving
the hierarchical relationships among these elements. For each
section, we retain subelements named
section or title; but for each
title, we retain the full content of the element. This
might be accomplished by the following recursive function:

The "skeleton" of a given document, containing only its sections
and titles, can then be obtained by invoking the
local:sections-and-titles function on the root node of
the document, as follows:

local:sections-and-titles(fn:doc("cookbook.xml"))

As another example of a recursive transformation, suppose that
we wish to scan over a document, transforming every attribute named
color to an element named color, and
every element named size to an attribute named
size. This can be accomplished by the following
recursive function (note that the element constructor in case
$e generates attributes before child elements):

The transformation can be applied to a whole document by
invoking the local:swizzle function on the root node
of the document, as follows:

local:swizzle(fn:doc("plans.xml"))

I.4
Selecting Distinct Combinations

It is sometimes necessary to search through a set of data to
find all the distinct combinations of a given list of properties.
For example, an input data set might consist of a large set of
order elements, each of which has the same basic
structure, as illustrated by the following example:

From this data set, a user might wish to find all the distinct
combinations of product, size, and
color that occur together in an order.
The following query returns this list, enclosing each distinct
combination in a new element named option:

J
Guidance for Handling of Modules (Non-Normative)

This specification gives considerable flexibility to
implementations in the way that modules are implemented, in
particular, in the way that module URIs and their location URIs are
interpreted. This flexibility is intentional, because XQuery
implementations are designed to operate in a wide variety of
environments, and some of those environments impose constraints.
Nevertheless, in the interests of interoperability, the Working
Group hopes that it will be useful to offer some suggestions for
how implementations might choose to interpret the specification, in
the absence of implementation factors that make a different
interpretation necessary.

J.1 Module URIs

Generally, Module URIs should be treated in the same way as
other namespace URIs.

Query authors should use a string that is a legal absolute IRI.
Implementors should accept any string of Unicode characters. Module
URIs should be compared using the Unicode codepoint collation
rather than any concept of semantic equivalence.

Implementations may provide mechanisms allowing the module URI
to be used as input to a process that delivers the module as a
resource, for example a catalog, module repository, or URI
resolver. For interoperability, such mechanisms should not prevent
the user from choosing an arbitrary URI for naming a module.

Similarly, implementations may perform syntactic transformations
on the module URI to obtain the names of related resources, for
example to implement a convention relating the name or location of
compiled code to the module URI; but again, such mechanisms should
not prevent the user from choosing an arbitrary module URI.

As with other namespace URIs, common practice is often to use
module URIs whose scheme is "http" and whose authority part uses a
DNS domain name under the control of the user.

The specifications allow, and some users might consider it good
practice, for the module URI of a function library to be the same
as the namespace URI of the XML vocabulary manipulated by the
functions in that library.

J.2 Multiple Modules with
the same Module URI

The specifications allow several different modules with the same
Module URI to participate in a query.

Although other interpretations are possible, it is suggested
that in such cases implementations should require the names of
global variables and functions to be unique within the query as a
whole: that is, if two modules with the same module URI participate
in a query, the names of their global variables and functions
should not overlap.

If one module contains an "import module" declaration for the
module URI M, then all global variables and functions declared in
participating modules whose module URI is M should be accessible in
the importing module, regardless whether the participation of the
imported module was directly due to this "import module"
declaration.

There should only be one instance of a global variable with any
given name. For example, if a global variable V is initialized
using an element constructor, then there should only be one
instance of this element, even if the module in which V is declared
is imported by several other modules.

(A different approach to this might be used in an environment
where a group of modules can be compiled as a unit; in such cases a
module used within the compiled unit might be considered distinct
from an instance of the same module imported from elsewhere in the
query.)

J.3 Location URIs

The term "location URIs" is used here to refer to the URIs in
the "at" clause of an "import module" declaration.

Products should (by default or at user option) take account of
all the location URIs in an "import module" declaration, treating
each location URI as a reference to a module with the specified
module URI. Location URIs should be made absolute with respect to
the static base URI of the query module containing the "import
module" declaration where they appear. The mapping from location
URIs to module source code or compiled code MAY be done in any way
convenient to the implementation. If possible given the product's
architecture, security requirements, etc, the product should allow
this to fetch the source code of the module to use the standard web
mechanisms for dereferencing URIs in standard schemes such as the
"http" URI scheme.

When the same absolutized location URI is used more than once,
either in the same "import module" declaration or in different
"import module" declarations within the same query, a single copy
of the resource containing the module should be loaded. When
different absolutized location URIs are used, each should result in
a single module being loaded, unless the implementation is able to
determine that the different URIs are references to the same
resource. No error due to duplicate variable or functions names
should arise from the same module being imported more than once, so
long as the absolute location URI is the same in each case.

By default, implementations should report a static error if a
location URI cannot be resolved. However, this is not intended to
disallow recovery strategies being used if appropriate.

J.4 Cycles

It is not an error to have a cycle in the import graph, either
at the level of module URIs or at the level of location URIs. The
only rules concerning cycles affect the relationships between
functions and variables defined in different modules.

K Revision
Log (Non-Normative)

26 Oct 2009

Added support for higher order functions.

Applied all XQuery 2ed errata.

Eliminated BindingExpression production - see
http://www.w3.org/Bugs/Public/show_bug.cgi?id=6921.

Fixed two typos in Binary Operators table - see
http://www.w3.org/Bugs/Public/show_bug.cgi?id=7048

Changed syntax of outer for, which now uses the
AllowingEmpty production in the for
clause.

Added support for private functions. Decided at meeting 381
(http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2008Oct/0152.html).

Changed introductory text on the relationship between XQuery and
XPath to list the cases where a syntactically valid query can
return different results in the two languages - see
http://www.w3.org/Bugs/Public/show_bug.cgi?id=7163.

Added note to illustrate the difference between grouping in SQL,
which reduces the equivalent of a non-grouping variable to one
representative value, and grouping in XQuery, which binds each
non-grouping variable to a sequence containing the concatenated
values of that variable in all the pre-grouping tuples that were
assigned to that